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Trump says whistleblower has ties to a Democratic rival. Here's what we know.

"Our client has never worked for or advised a political candidate, campaign, or party," the still-unnamed whistleblower's attorney said.

President Donald Trump claimed Wednesday that the intelligence community whistleblower whose complaint led to an impeachment inquiry has ties to his Democratic "opponents," a charge met with pushback from the still-anonymous person's lawyer.

"The Whistleblower's facts have been so incorrect about my 'no pressure' conversation with the Ukrainian President, and now the conflict of interest and involvement with a Democrat Candidate, that he or she should be exposed and questioned properly. This is no Whistleblower," Trump said in a tweet Wednesday morning.

"The Whistleblower's lawyer is a big Democrat. The Whistleblower has ties to one of my DEMOCRAT OPPONENTS. Why does the ICIG allow this scam to continue?" he continued.

Trump and some Republican allies, including Ohio Rep. Jim Jordan and South Carolina Sen. Lindsey Graham, have previously said the identity of the whistleblower whose complaint galvanized an impeachment inquiry should be made public, even though whistleblower laws protect requests for confidentiality.

Mark Zaid, an attorney for the whistleblower, called the identity of his client "irrelevant" — but responded Wednesday evening to what he said were "ongoing efforts to mischaracterize whistleblower #1's alleged 'bias' in order to detract from the substance of the complaint."

Beyond Zaid's comments — and what Inspector General of the Intelligence Community Michael Atkinson wrote in a letter released to the public on Sept. 26 — not much else is known about the still-anonymous person who wrote the complaint. That letter, addressed to acting Director of National Intelligence Joseph Maguire and dated Aug. 26, raised the appearance of bias.

What the letter said about the whistleblower's politics

Atkinson wrote to Maguire that he considered an "indicia of an arguable political bias on the part of the Complainant in favor of a rival political candidate" in considering the complaint's credibility.

But Atkinson, a Trump appointee, determined that this did not change the facts surrounding the issue, “particularly given the other information the ICIG obtained during its preliminary review” of the complaint. He concluded the complaint was "credible" and of "urgent concern."

While a Congressional investigation is ongoing, Atkinson is the first person who will have had a chance to evaluate the complaint. Attorneys who represent whistleblowers told NBC News last week that once a complaint is filed, the internal watchdog is charged with reviewing its credibility, which might mean reviewing documents and interviewing witnesses to check for corroborating information.

Trump's allegations

Trump's tweets Wednesday also alleged "involvement with a Democratic candidate," citing media reports not confirmed by NBC News.

Zaid, responding Wednesday, said the whistleblower "never worked for or advised a political candidate, campaign, or party," and had spent their government career in apolitical roles in the executive branch.

"In these positions our client has come into contact with presidential candidates from both parties in their roles as elected officials—not as candidates," Zaid said, adding that the whistleblower "voluntarily provided relevant career information" to help Atkinson vet his complaint.

Testifying to Congress, Acting Director of the National Intelligence Joseph Maguire said he had "every reason to believe that they have done everything by the book and followed the law."

Sen. Chuck Grassley, R-Iowa, who helped write the whistleblower protection laws, agreed, breaking with many in his party to admonish politicians and media commentators "for uninformed speculation" wielded by "a partisan weapon."

But some of Trump's allies have made it clear they are not satisfied.

Sen. Tom Cotton, R-Ark., wrote a stinging letter to Atkinson Wednesday, demanding details on the "arguable political bias" he'd referenced in his August letter to Maguire.

"This information is urgently relevant for the American people and their elected representatives to evaluate the complainant’s credibility and to determine whether the House’s so-called impeachment inquiry has been, in reality, a well-coordinated partisan attack from the beginning," Cotton wrote.

Trump's other claims

There's no evidence that the whistleblower complaint was "so incorrect," as Trump said, and in fact many of the allegations have been corroborated publicly since his complaint. A White House summary of Trump's July call with Ukraine's president at the center of report confirmed much of the whistleblower's account, even though the whistleblower was not on the call himself.

"I would say the whistleblower's complaint is in alignment with what was released yesterday by the president," Maguire told Congress during testimony on Sept. 26.

A second whistleblower came forward with information about Trump’s call with the president of Ukraine earlier this month. Zaid said that the second whistleblower "has first-hand knowledge" of the events.

Trump also claimed that Zaid is a "big Democrat;" Zaid wrote on Twitter that he is a registered political Independent who has represented members of Congress on both sides of the aisle. He added that he represented the Republican National Committee in a suit involving Hillary Clinton emails.