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Sanders vs. Warren is shaping up to be quite the fight

First Read is your briefing from "Meet the Press" and the NBC Political Unit on the day's most important political stories and why they matter.

MIAMI – Bernie Sanders and Elizabeth Warren won’t be sharing the same presidential debate stage here – Warren participates on Wednesday night, while Sanders goes on Thursday.

Still, they’re engaged in quite the progressive primary on the left side of the Democratic field.

As Warren has crept up in the polls – and skyrocketed in a new MoveOn straw poll – Sanders has tried to one-up her on policy, by unveiling a plan that would pretty much wipe away all student debt.

And it’s reminder: Who finishes ahead of whom in Iowa in this progressive fight will be a finalist for the Democratic nomination.

Maybe not the overall frontrunner – because that person will need to be able to consolidate the African-American vote in South Carolina and the South at large.

But definitely one of the last two or three men/women standing.

So it’s fitting that one of them (Warren) will be at the center of attention on Wednesday night, while the other (Sanders) will join Joe Biden in the middle on Thursday.

Democrats’ immigration dilemma: House Democrats have a difficult choice to make.

Do they appropriate money to deal with the humanitarian crisis on the border? Even if they don’t trust how the Trump administration might use that money?

“Congress is trying to rush $4.5 billion in emergency humanitarian aid to the southwestern border while placing new restrictions on President Trump’s immigration crackdown, spurred on by disturbing images of suffering migrant families and of children living in squalor in overcrowded detention facilities,” the New York Times writes.

“But with a House vote on the package planned for Tuesday, some Democrats are revolting over the measure, fearing that the aid will be used to carry out Mr. Trump’s aggressive tactics… Republicans are siding with the White House, which on Monday threatened a veto. They oppose restrictions in the measure that are meant to dictate better standards for facilities that hold migrant children and to bar the money from being used for enforcing immigration law.”

2020 Vision: Gideon to take on Susan Collins in Maine

The Dem effort to retake control of the U.S. Senate in the 2020 elections got a boost on Monday when Sara Gideon, speaker of the Maine House, said she was challenging Sen. Susan Collins, R-Maine.

“Susan Collins has been in the Senate for 22 years. And at one point, maybe she was different than some of the folks in Washington. But she doesn't seem that way anymore,” Gideon said in her announcement video.

She added, “And Susan Collins' vote to put Brett Kavanaugh on the Supreme Court may be paying off for her, but it's put women's control over their own health-care decisions in extreme jeopardy."

Remember, Democrats need to gain a net pickup of three seats to win back the Senate (if they also win the White House) – so Colorado, Arizona and Maine.

And if Dem Sen. Doug Jones loses in Alabama, they’ll need to win in one more state – North Carolina, Georgia, Iowa or Texas.

So having a piece on the board in Maine is essential.

On the campaign trail today

Vice President Pence headlines a “Latinos for Trump Coalition” in Miami ahead of the Dem debates that begin tomorrow in the city… Elizabeth Warren holds a town hall in Miami… So does Beto O’Rourke… Jay Inslee talks about the environment in the city… And both Julian Castro and John Delaney hold separate media avails.

Data Download: And the number of the day is … 49 percent

That's the share of residents of the Miami-Fort Lauderdale area who say in a new poll that they have made physical changes to their homes in the last year to protect against sea-level rise, flooding or extreme weather.

That's compared to 30 percent of other Florida residents.

The new online survey by Climate Nexus, in partnership with the Yale Program on Climate Change Communication and the George Mason University Center for Climate Change Communication, also found that 71 percent of Florida voters support government action to address climate change.

Tweet of the day: The Ayatollah of Rock-n-rolla

The Lid: Apples to apples

Don't miss the pod from yesterday, when guest star Alex Seitz-Wald walked us through his latest puzzling on what "electability" is all about.

ICYMI: New clips you shouldn’t miss

Congress is trying to rush $4.5 billion in emergency aid to migrants on the border – but it's getting complicated quickly, and the bill remains in limbo.

In an interview with The Hill, Trump denied the most recent accusation of sexual assault against him, calling his latest accuser "not my type"

The New York Times offers a deep dive into Elizabeth Warren's early life.

Iran says the path to diplomacy is closed after "outrageous" new sanctions.

Ali Vitali reports that, after missing the debate cut, Seth Moulton will be up with ads during the broadcasts.

And NBC’s Monica Alba writes about the RNC’s counter-programming efforts in Miami.

TRUMP AGENDA: Another stiff-arm to oversight

The White House directed Kellyanne Conway not to testify before a House panel.

The Supreme Court has allowed a trademark for a brand name that sounds a lot like a word we definitely can't print in this family newsletter.

POLITICO writes that Trump's relationship with Mick Mulvaney is on the rocks.

2020: Under Pressure

Kamala Harris is facing pressure to get more personal on the trail.

Our colleagues at NBC Latino look at how both sides in 2020 are eying the Latino vote in Florida.

Bernie Sanders is figuring out how to deal with the rise of Elizabeth Warren.

Warren is leading a new poll.

POLITICO's lead story today: "Joe Biden keeps stepping in it – and voters couldn’t care less."

Michael Bennet has added a pollster and two media strategists to his team.

What's up with those rumored Mike Pompeo Senate ambitions?