WASHINGTON (BLOOMBERG) - Donald Trump called on his administration to stop hiring "Never Trumpers," after a parade of current and former aides added fuel to a House impeachment inquiry with damaging testimony about the president's actions towards Ukraine.

He singled out William Taylor, the acting US ambassador to Ukraine who in testimony on Tuesday assailed the president's cultivation of an "irregular policy channel" with Kyiv led by his personal attorney, Rudy Giuliani.

"Never Trumper Republican John Bellinger, represents Never Trumper Diplomat Bill Taylor (who I don't know), in testimony before Congress! Do Nothing Democrats allow Republicans Zero Representation, Zero due process, and Zero Transparency," Trump said in a series of tweets on Wednesday (Oct 23).

"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. Nothing good will ever come from them!"

Taylor recounted that it was Secretary of State Michael Pompeo who personally asked him to serve as acting ambassador after the previous envoy, Marie Yovanovitch, was recalled to Washington after running afoul of Trump and Giuliani.

While Taylor said he initially hesitated to take the job, he decided to accept it after Pompeo "assured me that the policy of strong support for Ukraine would continue and that he would support me in defending that policy."

Taylor testified Tuesday that a senior diplomat told him in early September that Trump made US security aid to Ukraine entirely dependent on a public promise to investigate Joe Biden and a conspiracy theory regarding alleged Ukrainian interference in the 2016 election.

The account offers what may be the most damaging revelations so far in the House impeachment investigation.