"Never Trumper Republican John Bellinger, represents Never Trumper Diplomat Bill Taylor (who I don’t know), in testimony before Congress!" Trump tweeted.

Trump's claim that he did not know Taylor came despite the fact that Secretary of State Mike Pompeo personally recruited Taylor for the post after the president’s initial ambassador to Ukraine was forced out due to pressure over a perceived anti-Trump bias.

Trump did not offer any evidence to support his allegation that Taylor, a career civil servant who has served in both Democratic and Republican administrations, harbored any anti-Trump bias. The attack landed as Taylor remains a part of Trump's State Department.

Last week, Taylor and another witness in the impeachment probe, former Pompeo aide Michael McKinley, retained Bellinger, who served in the Bush administration, according to NBC News. Bellinger was an outspoken Trump critic in the lead-up to the 2016 election, and told Foreign Policy last year he had no regrets about authoring a 2016 letter in opposition to Trump.

Ambassador William Taylor offered impeachment investigators damaging details of the president's foreign dealings. | J. Scott Applewhite/AP Photo

Trump also continued to rail against Democrats’ closed-door deposition process for the initial stages of their investigation, tweeting that “Do Nothing Democrats allow Republicans Zero Representation, Zero due process, and Zero Transparency” and decrying the proceedings as unfair.

“Even though there was no quid pro quo,” he claimed, “I’m sure they would like to try. Worse than the Dems!”

He then appeared to fire off a warning shot at other administration officials looking to lawyer up with “never Trumpers."

“It would be really great if the people within the Trump Administration, all well-meaning and good (I hope!), could stop hiring Never Trumpers, who are worse than the Do Nothing Democrats,” he wrote, adding that “Nothing good will ever come from them!”

Earlier Wednesday, the president claimed that though anti-Trump Republicans are supposedly “on respirators with not many left,” in his view, they posed a greater threat to the country than his Democratic opponents did.

“Watch out for them, they are human scum!” he added.

The intraparty fire from the president underscored several rough weeks for the GOP, which saw blowback from Republican lawmakers over Trump's foreign policy moves in Syria, his comparison on Tuesday of the impeachment probe to a "lynching," and the damaging testimony from Taylor.

Trump's new line of attack on key figures in the impeachment investigation also came as dozens of House Republicans, railing against the entirely closed-door proceedings thus far, banded together Wednesday morning to storm the secure room where depositions of impeachment witnesses were being held. Their protest brought Wednesday’s proceedings to a standstill for hours.

Republicans have repeatedly lodged complaints about how their counterparts have handled the impeachment process, taking issue with the lack of a formal House vote on the matter, though such a step is not required, and Democrats’ decision to first question witnesses in privacy before holding public hearings in order to prevent witnesses from aligning their testimony.

Republicans have also cried foul about an inability to summon their own witnesses for the inquiry or for White House lawyers to sit in on depositions, calling the treatment a violation of due process.