WASHINGTON, D.C. — President Donald Trump’s attorneys ignored explosive claims by former national security adviser John Bolton when they resumed their defense Monday in the Senate impeachment trial, arguing instead that Democrats had mischaracterized the president’s actions in Ukraine.

“We do not deal with speculation, allegations,” said Jay Sekulow, one of the president’s lawyers, insisting that Trump was justified in asking Ukraine to launch investigations that would benefit him politically, a request at the heart of the impeachment charges.

“Asking for a leader to get to the bottom of allegations of corruption is not a violation of oath,” Sekulow said in brief comments before handing off to Kenneth W. Starr, another lawyer for Trump and the former independent counsel who spearheaded the investigation that led to President Bill Clinton’s impeachment in 1998.

“Instead of a once-in-a-century phenomenon,” he lamented, “presidential impeachment has become a weapon to be wielded against one’s political opponent.”

Bolton reportedly wrote in a draft of a memoir of his time in the White House that Trump told him in August that he had blocked U.S. military aid to Ukraine in an effort to get the newly elected president there to investigate Trump’s political rival, former Vice President Joe Biden.

The report sent tremors through Capitol Hill as the nation’s third presidential impeachment trial began its second week.

Sen. Mitt Romney, R-Utah, told reporters that “it’s increasingly likely” that there will be enough votes to subpoena Bolton as a witness, as Democrats have demanded.

Sen. Susan Collins, R-Maine, another key moderate, said the report “strengthens the case for witnesses and have prompted a number of conversations among my colleagues.”

Even Sen. Lindsey Graham, R-S.C., a firm Trump ally who has opposed having any witnesses, suggested he would be open to some kind of agreement to bring in witnesses.

“If there is a desire and decision by the Senate to call Democratic witnesses, then at a minimum the Senate should allow President @realDonaldTrump to call all relevant witnesses he has requested,” Graham tweeted.

Other Republicans tried to downplay Bolton’s claims, saying they presented nothing new or weren’t to be automatically trusted.

Asked if believes Bolton, Sen. John Kennedy of Louisiana said, “I wouldn’t bet my house on it” and criticized the media frenzy surrounding the impeachment trial.

“I think everybody ought to pop a Zoloft, take their meds, and let’s wait and finish up,” Kennedy said.

Speaking to reporters before the trial resumed, Sen. Charles E. Schumer, the Senate minority Leader, called leaks about Bolton’s book “stunning.”

“It goes right to the heart of the charges against the president,” said Schumer, D-N.Y. “Ambassador Bolton essentially confirms the president committed the offenses charged in the first article of impeachment.

“We’re all staring a White House cover-up in the face,” Schumer said, adding that if Senate Republicans decide against calling witnesses, “they’re going to be part of the cover-up too.”

Trump repeatedly denied the allegations, telling reporters at the White House that they were “false.”

“I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens,” he tweeted shortly after midnight. “In fact, he never complained about this at the time of his very public termination. If John Bolton said this, it was only to sell a book.”

The president’s team has staked its defense in part on denying any link between the events at the heart of the impeachment case, which alleges that Trump abused his power by pressuring a foreign government to help his reelection campaign — and then obstructed Congress by ordering aides not to testify or provide documents.

Trump’s lawyers also have repeatedly declared that no witness had firsthand knowledge of a direct link between the White House order to withhold $391 million in congressionally authorized security aid and Trump’s push for Ukraine to announce an investigation of Biden, who is running for the Democratic presidential nomination, and his son.

After giving an abbreviated defense on Saturday, Trump’s lawyers were expected to shift the focus Monday toward Biden and Hunter Biden, who served on the board of a Ukrainian gas company. They’ve tried to portray the Bidens as corrupt in order to justify Trump’s request for Ukraine to investigate them. The Bidens have denied any wrongdoing.

For his part, Starr argued that the country had foolishly entered “the age of impeachment.”

“How did we get here?” he complained as he chronicled the history of the law and politics from President Richard Nixon’s resignation in the face of threatened impeachment to Clinton’s impeachment decades later.

“Like war, impeachment is hell. Or, at least, presidential impeachment is hell,” Starr said. “Those of us who lived through the Clinton impeachment, including members of this body, full well understand that a presidential impeachment is tantamount to domestic war, but thankfully protected by our beloved First Amendment, a war of words and a war of ideas. But it’s filled with acrimony and it divides the country like nothing else.”

After defense arguments are finished, senators will get 16 hours to submit written questions followed by an opportunity to debate whether witnesses should be called. That debate could occur as soon as Thursday.

Bolton has offered to testify to the Senate if he is subpoenaed. He had resisted a request from the Democratic-controlled House during the impeachment proceedings there.

It’s still unclear if four Republicans will join Senate Democrats to subpoena Bolton and possibly other witnesses.

Trump and Senate Majority Leader Mitch McConnell of Kentucky have sought to ensure a speedy path to acquittal without any witnesses.

Trump could try to block the testimony from his former national security adviser on the basis of executive privilege, which allows presidents to keep confidential their deliberative conversations with aides. But it’s not clear that Trump has any enforcement provisions if Bolton decides to honor a Senate subpoena.

Democrats say a claim of executive privilege would fail because Bolton has already written his story in his book draft, which was submitted to the White House for classification review on Dec. 30 and is scheduled to be published in March, and because executive privilege is not a shield for presidential wrongdoing.

“Senators should insist that Mr. Bolton be called as a witness, and provide his notes and other relevant documents,” the House impeachment managers said in a joint statement Sunday after The New York Times reported the details from Bolton’s manuscript. “The Senate trial must seek the full truth and Mr. Bolton has vital information to provide.”

Bolton could have additional evidence in his possession as well.

“He is known to be a voracious note taker,” said a Democratic aide working on the impeachment trial, and may have a “contemporaneous account” of his conversations with Trump on Ukraine.

Unlike some who testified during House impeachment hearings, Bolton is a Republican establishment figure with government service dating back to President Ronald Reagan’s administration. His hawkish views and sharp elbows in bureaucratic battles made him controversial, but he’s respected by many high-profile Republicans.

Romney called Bolton a “brilliant man” when Trump fired him in September after disputes over the president’s policy in Syria, North Korea and other parts of the world.

McConnell also praised Bolton at the time.

“I always appreciated John’s candor and clear advice,” he said.