An angry President Trump lashed out on Twitter Wednesday against top Democrats leading the impeachment investigation, saying they’re wasting everyone’s “time and energy on bull----.”

In a series of tweets, Trump took House Intelligence Committee Chairman Adam Schiff and House Speaker Nancy Pelosi to task, calling Schiff a “lowlife” and saying Pelosi isn’t capable of working on issues important to the American people.

Schiff received a heads-up even before the whistleblower complaint that led to the impeachment inquiry was filed, explaining how he knew to press for details. Trump reacted to that revelation by calling Schiff a "fraud."

The tirade came as Democrats prepared to take the first testimony in their investigation into whether Trump abused his office when he asked Ukraine to help smear former Vice President Joe Biden, seen as the leading contender for the 2020 Democratic presidential nomination.

“The do-nothing Democrats should be focused on building up our country, not wasting everyone’s time and energy on bull----,” Trump raged.

He again accused Democrats of trying to undue the results of the 2016 election, which saw Trump win the electoral vote but lose the popular vote, calling the impeachment investigation “nonsense” and blaming it for recent stock market losses. On Tuesday, he described the impeachment inquiry as a "coup."

The impeachment inquiry was triggered by the administration handling of a whistleblower complaint over a call Trump made to his Ukrainian counterpart just days after freezing military aid to the country fighting off Russian aggression. During that call, Trump asked Ukraine President Volodymyr Zelensky for a “favor,” asking for a full investigation of long-debunked allegations against Biden.

House Oversight Committee Chairman Elijah Cummings of Maryland said the panel would subpoena White House if it does not turn over documents related to Ukraine by Friday.

“I do not take this step lightly,” Cummings wrote to committee members, the New York Times reported. “Over the past several weeks, the committees tried several times to obtain voluntary compliance with our requests for documents, but the White House has refused to engage with — or even respond to — the committees.”

Any subpoena likely will touch off a battle with the White House. The subpoena reportedly will seek evidence the White House tried to suppress any records pertaining to the Ukraine call.

The State Department’s inspector general was to brief lawmakers Wednesday about material reportedly relevant to the investigation. The Times said the briefing was to deal with copies of documents.

Secretary of State Mike Pompeo revealed he listened in on the July 25 Zelensky call. He also accused Democrats of trying to bully State Department staffers.

Schiff warned Pompeo against interfering with the investigation.

"They just need to know that, even as they try to undermine our ability to find the facts around the president's effort to coerce a foreign leader to create dirt that he can use against a political opponent, that they will be strengthening the case on obstruction if they behave that way," Schiff said at a press conference with Pelosi.

Both former U.S. Ambassador to Ukraine Marie Yovanovitch and former special envoy to Ukraine Kurt Volker have agreed to speak with the committee, Reuters reported. And Schiff said Sunday, the whistleblower also has agreed to testify.

“We’ll get the unfiltered testimony of that whistleblower,” Schiff said on ABC’s “This Week.”

A Morning Consult poll released Wednesday indicated more Americans favor impeachment than oppose it for the first time, 46% saying Congress should initiate impeachment proceedings compared to 43% who oppose such an inquiry. Support among Democrats was 80% compared to 9% of Republicans. Among Republicans, 49% said there is nothing Trump could do that would make them support impeachment.