WASHINGTON — House Democrats said Wednesday that they planned to subpoena the White House by Friday if it did not comply with broad requests for documents related to President Donald Trump’s efforts to pressure Ukraine into investigating a leading political rival, and any attempt by the administration to conceal his actions.

Rep. Elijah Cummings of Maryland, the chairman of the Oversight and Reform Committee, notified his panel of the impending subpoena on Wednesday. He said the White House had thus far ignored voluntary requests he submitted with the House Intelligence and Foreign Affairs committees.

“I do not take this step lightly,” Cummings wrote. “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.”

The threat came as the president lashed out at Democrats in aseries of angry outbursts online and before television cameras, denouncing leading lawmakers as “dishonest people” who were focused on overturning an election they lost in 2016.

With a visibly uncomfortable president of Finland sitting next to him in the Oval Office, Trump declared that Democrats were “guilty as hell” of corrupting the 2016 election, that former Vice President Joe Biden “is corrupt” and “less smart now than he ever was,” and that a CIA whistleblower is “a spy in my opinion.”

He saved his sharpest barbs for Rep. Adam Schiff, D-Calif., the chairman of the House Intelligence Committee, who has taken the lead in the investigations. Trump called him “a lowlife” and “shifty, dishonest guy.” Referring to Secretary of State Mike Pompeo, the president said Schiff “couldn’t carry his blank strap,” using the word “blank” instead of “jock” for a typical locker-room insult.

As he has for several days, the president focused intently on Schiff’s recent statement in which the congressman provided his interpretation of the president’s telephone call with the president of Ukraine, making clear that they were not Trump’s precise words but reflected his intent.

“He should resign from office in disgrace,” Trump said. “Frankly, they should look at him for treason because he is making up the words of the president of the United States.”

At a second appearance with the visiting President Sauli Niinisto of Finland, Trump became increasingly angry while responding to questions about the impeachment investigation — complaining that it was part of a “hoax” that has been perpetrated against him since he took office, and threatening vaguely to bring “a major lawsuit” to retaliate. He went after Schiff anew, and blasted House Speaker Nancy Pelosi, charging that she “hands out subpoenas like they’re cookies.”

Pelted with questions about his actions and the impeachment inquiry, the president repeatedly told reporters to ask Niinisto questions instead. At the end, Trump turned his back on the Finnish president and stalked off the stage in the East Room without offering his guest the customary handshake.

The clash between the president and congressional Democrats came on another momentous day in Washington where, in just over two weeks, revelations about attempts by Trump and his personal lawyer, Rudy Giuliani, to pressure Ukraine to investigate Biden and other Democrats have exploded into an impeachment inquiry that threatens his presidency.

Pelosi and Schiff warned the Trump administration that any attempt to stonewall the House’s request or intimidate witnesses would be construed as obstruction worthy of impeachment itself.

“We’re not fooling around here,” Schiff said. “We don’t want this to drag on months and months and months, which would be the administration’s strategy. So they just need to know 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.”

After asserting that Congress would not let impeachment entirely eclipse its legislative agenda, Pelosi accused the president of an “assault on the Constitution.”

The impeachment inquiry is escalating rapidly. In the past week, the House has issued two subpoenas for records. Cummings’ warning suggested that lawmakers and their staffs were working to collect the evidence they believe they need to corroborate the anonymous CIA whistleblower’s complaint that touched off their inquiry. First, they targeted the State Department, then Giuliani and now the White House.

At the same time, lawmakers were preparing to hear a mysterious bit of new information abruptly offered by the State Department’s independent watchdog, which could add a fresh twist to the inquiry. Steven Linick, the State Department’s inspector general, was to brief lawmakers in the afternoon about urgent material he signaled could be relevant to the investigation.

What exactly Linick intended to share with Congress remained a matter of intense speculation on Wednesday. Linick, who was not believed to be investigating the Ukraine matter himself, contacted lawmakers early Tuesday afternoon and extended a cryptic and urgent invitation to meet the next day “to discuss and provide staff with copies of documents,” according to an invitation reviewed by the New York Times.

The draft subpoena circulated by Cummings suggests he is casting a wide net for potential records related to the Ukraine matter, and it is all but certain to touch off a battle with a White House that has a long history of refusing to comply with congressional requests.

It explicitly asks for records that could indicate whether the White House or other administration officials took steps to conceal or destroy the records to prevent Congress or the public from learning what had happened.

Among the documents requested are any recordings, transcripts, notes or other records related to a July phone call in which Trump pressed President Volodymyr Zelenskiy of Ukraine to conduct investigations that would bolster the American leader politically, or an earlier April call between the two men. It asks for a full list of White House staff members involved in or aware of the calls, any communications that refer to the July call and details about how the White House maintained records of the call.

The draft subpoena also directs the White House to hand over records of any calls with other foreign leaders referring to the topics Trump discussed with Zelenskiy; of meetings related to Ukraine; and of the decision to temporarily withhold $391 million in security aid from the country this summer at the same time Trump was pressing Zelenskiy.