At the time, Warren was blogging for Talking Points Memo and about as well known as a policy wonk can be — which is to say not very. She had expressed zero political ambition, never run for office and her only real brush with Washington ended years earlier in a demoralizing loss when Congress passed a bankruptcy bill over her objections.
Reid's Congressional Oversight Panel came with a memorable acronym, COP, but had little real power. It essentially had one job: "Submit reports."
Still, Warren said yes right away and so began "When Harry met Liz," a political saga that continues to this day.
"Everyplace she's been, she's been extremely good, for lack of a better way to explain it," the understated Reid told NBC News in an interview.
Warren said in a statement, "Since then, we've been fighting the good fight — and Harry is someone you always want in your corner.”
Reid's call set in motion a series of events that would lead to her inspiring the creation of a new federal agency, election to the Senate and an eventual run for the presidency, rising to the top of the Democratic field — with Reid as a powerful champion at key points along the way.
While Warren came to Washington just weeks after the election of Barack Obama, it was Reid who first plucked her from relative obscurity in academia and later championed her Senate bid.
"He would always ask about her," said Guy Cecil, who ran the Democratic Senatorial Campaign Committee at the time and is now chairman of the party's largest super PAC, Priorities USA. "And he was always much more bullish on her than a lot of people in Massachusetts."
It was Reid who promoted Warren in the Senate after she was elected in 2012, first by giving her the spot she wanted on the powerful Banking Committee, then by creating a position for her on his leadership team, despite objections from some longer-serving senators.
"There was a tussle," said former Reid adviser Jim Manley of the move to put her on leadership. "Not everyone was happy when she was named to it."
Reid, in the interview with NBC News, revealed he thought so highly of Warren that he wanted Hillary Clinton to pick her as a running mate in 2016 — and he even personally lobbied Bill Clinton on it.
"I thought that having two women would be a very very unique and powerful message,” Reid said. "I talked to President Clinton and went and spent a good part of the afternoon with him and felt comfortable that he liked idea. And I'm sure he did. But I guess with all the staff that's involved with a presidential team that they overrode me and him."
Reid had powerhouse Democratic law firm Perkins Coie draw up a memo exploring Massachusetts' Senate vacancy laws so he could move to replace Warren as quickly as possible if she were chosen for the No. 2 slot, according to a former senior Reid aide.
That didn't work out, but, once again, Reid was there, urging Warren to run for president herself in the wake of Clinton's loss in 2016 to Donald Trump, according to multiple people close to both.
"Harry Reid was among the first people in D.C. to recognize the unique credibility and voice Elizabeth Warren brought to the table," said Adam Green, a Warren ally who runs the Progressive Change Campaign Committee. "Reid asking her to hold accountable the big banks and the government after the Wall Street bailout was key to Warren's rise — and the path to her presidential campaign can be traced back to that key trajectory-changing moment."
The Mormon ex-cop who started his career as a conservative Democrat may make for an unlikely match with the crusading progressive Ivy League prof.
But they shared hardscrabble roots in the American West and the economic populism of Franklin Delano Roosevelt. Warren keeps a bust of FDR in her Senate office while Reid has recalled how one of his mother's few prized possessions was a pillowcase embroidered with an FDR quote that hung on the wall of their ramshackle house that lacked indoor plumbing.
"He loves someone with a good story. Someone who's overcome hardship like he has, someone who's worked their ass off like Elizabeth Warren has," said Rebecca Katz, a Democratic strategist who used to work for Reid. "When he believes in you, he will fight for you."
And after Reid named her to the oversight panel, he felt invested in her career.
"He's very proud of that appointment," said David Krone, Reid's former chief of staff. "To this day, he takes great pride in it."
Now, Reid could be a valuable ally in his native Nevada, an early voting presidential state with caucuses in February, where he keeps tabs on the political machine he built, even after his retirement from the Senate in 2017 and declining health.
The 79-year-old former Senate leader has pledged to remain neutral in Democratic presidential primaries and he has friends in the field, including several senators with whom he served.
But most of his former aides involved in the 2020 race are either working for Warren or Vermont Sen. Bernie Sanders, reflecting Reid's own leftward evolution over his long career in the Senate.
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He keeps in touch with many of his former aides via text message, and occasionally hears complaints from them, like after he knocked "Medicare for All" in an interview.
Reid also speaks with the candidates directly, including Warren, who has visited him this year.
"Reid keeps his poker face on who he will endorse, but in my heart, I have no doubt which side he's on," said one person who has been in communication with Reid.
Why Reid chose Warren in those dizzy early days of the financial crisis and Great Recession remains a bit of a mystery, even to people close to both Democrats.
Was it Sen. Ted Kennedy, whom Warren had gotten to know in Massachusetts, who pushed for her? Or was it Reid's staff, who were early adopters of the nascent progressive blogosphere, which Warren was a part of? Or maybe some other senator who had gotten to know Warren during the earlier bankruptcy fight?
In the interview, Reid insisted he discovered Warren on his own.
A voracious reader, Reid said he had come across a review of one of Warren's books, which had re-entered the zeitgeist in the wake of the financial crisis. He read it and explored her other writings.
Reid was impressed by her intelligence, ferocity and ability to translate complex economic issues into plain English.
"So out of the blue, I called her at her home," Reid said. "I had never met her. I called her cold at her home."
Looking back on what that appointment led to, Reid added, "That was a break for her, and I think for the country."
While Reid gave her the job on COP, Warren herself turned it into a launching pad.
"She was known before that, but known in the way that can't be expressed as a percentage of the population because it's too small a number," said former North Carolina Democratic Rep. Brad Miller, who worked with Warren on financial reform efforts.
"She had been delivering the same sermon for years, but she suddenly had a pulpit," he added.
At their inaugural meeting in the winter of 2008, the five members of the oversight panel elected Warren their chairman.
The first field hearing was in Las Vegas, at the request of Reid, who singled out Warren for praise in his introductory remarks.
While the group's only real requirement was to compile a report for Congress every 30 days on how the Treasury Department was spending the $700 billion Congress had given them, Warren turned those updates into media events.
She would do rounds of interviews and uploaded videos of herself the new web-service called YouTube, explaining what was happening in the economy and the government's response in a way average Americans could understand.
"The country was awash in news programs featuring financial experts who spoke about the crisis using language that to most people sounded like gibberish," she wrote in her book. "The explanations offered by the talking heads all had the same subtext: Only the insiders are smart enough to understand what's really going on, so just trust us."
"Plain language," she continued, "was about blowing the bulls--- whistle" on that notion.
Her tenure on the panel started in the final months of George W. Bush's presidency in 2008 and continued into the Barack Obama era.
In public hearings, she questioned officials from both administrations with equal intensity on why, for instance, the government seemed more interested in saving the big banks than aiding homeowners facing foreclosure.
Some in the new Democratic administration did not take kindly to the treatment. Former Obama Treasury Secretary Timothy Geithner wrote in his memoir that Warren's hearings "felt more like made-for-YouTube inquisitions than serious inquiries" and called their relationship "complicated."
People were deeply anxious about the economy and how their taxpayer dollars were being used to fix it and she tapped into the populist discontent that would later lead to the Tea Party on one side and Occupy Wall Street on the other.
Time Magazine put her on their cover under the headline, "The New Sheriffs of Wall Street."
Jon Stewart invited Warren on "The Daily Show," the premier voice of liberal America at the time. She was so nervous she vomited minutes before going on air, but nonetheless managed to make an impact.
“That is the first time in six months to a year that I felt better," Stewart said on air. "That was like financial chicken soup for me. Thank you. That actually put things in perspective and made sense.”
But she was also making plenty of enemies who viewed her conduct as grandstanding.
"The left-wing blogosphere has applauded Warren's aggressive questioning of policymakers and emboldened her to become a crusader. It's also dangerous for the people on important commissions to give in to the populist groundswell," wrote Thomas Cooley, then dean of the New York University Stern School of Business in an op-ed for Forbes. "Their job is to keep a rational and clear-headed perspective in the public mind."
Warren's work on the oversight panel led directly to the next phase of her career — pushing for the creation of the Consumer Financial Protection Bureau.
Former Rep. Barney Frank, D-Mass., author of the Dodd-Frank financial reform act, said he'd never known Warren to express interest in elective office, but noticed something change in her around this time.
"I think the involvement on behalf of the bureau gave her a taste for it," Frank said. "It and made her realize she could get things done."
Warren wanted to run the agency she had just helped create and allies like Sanders urged Obama to appoint her — "I've known Elizabeth for many years. She's smart. She's tough. She's prepared to take on Wall Street," Sanders said at the time. The president wrestled with the question for months, but ultimately decided Republicans' all-out-opposition made her impossible to confirm in the Senate.
He needed someone to run against Republican Scott Brown in Massachusetts, who had won a shocking victory in a special election in to replace Kennedy, who died in office, in 2010.
Some Democrats doubted whether the surprisingly popular Brown was beatable, especially by an Oklahoma-born Harvard academic who had never won an election in a state that had never elected a woman senator.
But Reid pushed ahead, helping to convince both Warren and doubters in his party she could do it.
"I wanted to make sure that I did everything to get that Ted Kennedy seat back again," he said in the interview.
After she won, progressives pushed him to put Warren on the Banking Committee, despite considerable opposition from industry. Reid stayed mum in public, but in private he told aides, "I'd have to be the dumbest person in the world not to put her on Banking."
Two years later, he took the unusual step of promoting the freshman to be a part of his leadership teamdespite consternation from other members of the caucus about the rapid ascent of the progressive newcomer. "There was a lot of jealousy," said one former top Reid aide.
To placate moderates, Reid also appointed Virginia Sen. Mark Warner at the same time to leadership.
Tensions with the Obama administration would reignite again when now-Sen. Warren spoke out against his trade policy and helped torpedo several Obama nominees, including economist Larry Summers for Federal Reserve Chairman.
"Reid went out of his way to empower Warren at the same time the Obama administration was attacking her,” said Murshed Zaheed, a former Reid staffer.
And she was a team player for Reid, going out of her way to not blindside him.
One former senior Reid adviser could recall only one time Warren got contentious in a Senate leadership meeting, over Democratic support for a bill backed by the pharmaceutical industry. She might have caught others off guard in the room, but Reid knew what was coming. She had called him the weekend before to give him a heads-up.
Today, the two keep in touch, though they were never particularly close personally — Reid is not particularly close personally with too many people.
In the acknowledgments for Warren’s 2014 book, "A Fighting Chance," she thanks dozens of people, but Reid gets a special mention.
"I'm grateful to Majority Leader Harry Reid for the confidence he showed in a professor from Massachusetts to be part of the oversight group," she wrote. "Someday I hope he’ll tell me how it was that he picked me."
Alex Seitz-Wald is senior digital politics reporter for NBC News.