WASHINGTON — The White House said Friday it would not participate in House Democrats’ impeachment proceedings, relying instead on an aggressive counterattack in the Republican-controlled Senate, where President Trump’s allies are determined to not just acquit him but seek political retribution.

The decision was not unexpected, but it sharpened the White House’s focus on a potential Senate trial, which will occur if the full House votes to make Trump the third U.S. president ever impeached. That vote could take place before Christmas, with a trial in January.

“House Democrats have wasted enough of America’s time with this charade,” Pat Cipollone, Trump’s top White House lawyer, wrote to House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.). “You should end this inquiry now and not waste even more time with additional hearings.”

Nadler said later that Americans “deserve answers” from the president.

“We gave President Trump a fair opportunity to question witnesses and present his own to address the overwhelming evidence before us,” he said in a statement. “After listening to him complain about the impeachment process, we had hoped that he might accept our invitation.... Having declined this opportunity, he cannot claim that the process is unfair.”

The Judiciary Committee will hold its second impeachment hearing on Monday, and Nadler had given the White House a Friday deadline to disclose whether it would present a defense in coming hearings. The committee is expected to draw up articles of impeachment over the next week.

White House officials have held strategy sessions with key Republicans on Capitol Hill, and the heads of three Senate committees announced a parallel investigation Friday that could shift attention away from Trump’s alleged wrongdoing and onto possible Democratic misdeeds.

The three senators — Homeland Security Committee Chairman Ron Johnson (R-Wis.), Finance Committee Chairman Charles E. Grassley (R-Iowa) and Judiciary Committee Chairman Lindsey Graham (R-S.C.) — said they would investigate allegations that Ukrainian officials coordinated with the Democratic Party to undermine Trump in the 2016 election.

“There are many unanswered questions that have festered for years,” Johnson said.

The Republicans said they were not casting doubt on the conclusion from U.S. intelligence agencies that Russia’s government hacked Democratic computer networks during the 2016 presidential race. But their announcement lends credence to Trump’s attempts to downplay Moscow’s support for his campaign, which he denies.

Graham has also suggested the possibility of calling Hunter Biden, son of former Vice President Joe Biden, to testify about his lucrative work for Burisma, a Ukrainian gas company. The Bidens have denied any wrongdoing.

The impeachment inquiry revolves chiefly around Trump’s request in a July 25 phone call for “a favor” from Ukraine’s president, Volodymyr Zelensky, to investigate the Bidens and the 2016 election.

Shortly before the call, the White House had blocked $391 million in security aid that Congress had appropriated to help Ukraine fight Russian-backed insurgents.

Democrats have accused Trump of abusing his power by using foreign policy to boost his reelection campaign.

Trump’s camp sees a Senate trial as a chance to counter the flood of negative headlines that flowed out of the House impeachment hearings. A trial could allow Republicans to gain some control of the narrative and paint Democrats as abusing their power in an effort to punish Trump.

Brad Parscale, Trump’s campaign manager, said Democrats have always wanted to impeach the president, “so they should just get on with it so we can have a fair trial in the Senate and expose the swamp for what it is.”

Senate Majority Leader Mitch McConnell (R-Ky.) has said he wants to reach a deal on the rules for the trial with Senate Minority Leader Charles E. Schumer (D-N.Y.), but McConnell could try to force Republican rules through on a party-line basis.

The trial would be overseen by Chief Justice John G. Roberts Jr., who was nominated by a Republican president, George W. Bush.

Although acquittal in the Senate appears all but certain, Trump and his allies may need to temper their expectations for the proceedings.

Graham has left open the possibility of calling House Intelligence Committee Chairman Adam B. Schiff (D-Burbank), a Trump nemesis, to testify, but he poured cold water on demands to seek Schiff’s phone records.

“We’re not going to do that. When members start subpoenaing each other as part of oversight, the whole system breaks down,” he told reporters.

During a House Judiciary Committee hearing Wednesday, three constitutional scholars chosen by Democrats unanimously agreed that Trump’s efforts to get Ukraine to investigate his political rivals qualified as impeachable high crimes and misdemeanors.

A fourth scholar, selected by Republicans, said the president’s conduct was wrong but did not meet the high bar for impeachment. He argued that Democrats were rushing the process and needed more evidence.

Ken Gormley, president of Duquesne University in Pittsburgh and the author of books about the impeachment investigations of Richard Nixon and Bill Clinton, said it would be unwise for Trump to get too comfortable ahead of the Senate trial.

“Nothing is foreordained,” he said. “You don’t know what shoe is going to drop.”

He noted that Republican support for Nixon often appeared solid before the Supreme Court ordered the release in 1974 of secretly recorded Oval Office tapes, which revealed the president ordering a cover-up of the Watergate break-in. Nixon resigned soon after rather than face almost certain removal from office.

Gormley said impeachment is a “permanent stain” on a president’s legacy.

But Ross Garber, a Tulane University law professor and an expert on impeachment, said Trump could find a way to turn it into a campaign talking point as he runs for reelection next year.

“It may be an asterisk that a president ultimately doesn’t mind,” he said. “If the vote is as partisan as it’s shaping up to be, it may be an asterisk that Trump wears proudly and portrays as a consequence of him being a disruptor.”

Trump has offered no cooperation with House Democrats’ impeachment proceedings.

The White House has directed senior officials not to testify, and the State Department and other agencies have refused to turn over subpoenaed documents. The president’s personal lawyer, Rudolph W. Giuliani, has also defied a subpoena.

Trump has said he wanted his aides to testify but blamed Democrats for holding “very unfair hearings.”

It’s possible that Democrats could include obstruction of Congress as a potential article of impeachment. Noah Feldman, a Harvard University law professor who testified Wednesday, said Trump’s behavior “undermines the basic principle of the Constitution.”

Times staff writer Sarah

D. Wire in Washington contributed to this report.