The clash over President Trump's explosive but still unproven claim that he was targeted for surveillance by the Obama administration will be in the spotlight Monday when FBI Director James B. Comey testifies before the House Intelligence Committee.
Comey has come under growing pressure from lawmakers to say publicly whether the FBI conducted wiretapping or other secret surveillance of Trump or his associates before or after the 2016 election as part of a criminal inquiry or a counterintelligence investigation.
The Republican and Democratic leaders of the Senate and House intelligence committees told reporters last week that they have seen no evidence to support Trump's claims that the Obama administration had wiretapped him at Trump Tower.
"I hope that we can put an end to this wild-goose chase because what the president said was just patently false," Rep. Adam B. Schiff (D-Burbank), the ranking Democrat on the House Intelligence Committee, told NBC's "Meet the Press" on Sunday. "And the wrecking ball it created now has banged into our British allies and our German allies, it's continuing to grow in terms of damage, and he needs to put an end to this."
In a statement Friday, the Justice Department said it had complied with requests from leaders of the House and Senate intelligence committees and judiciary committees "seeking information related to surveillance during the 2016 election."
The statement did not say whether the FBI had uncovered any surveillance that targeted Trump or inadvertently captured him while targeting someone else.
Trump first accused Obama on March 4 of wiretapping him and has refused to back down, insisting that he will be proved right. A spokesman for Obama described the claim as "simply false," and no evidence has emerged to support it.
On Friday, at a news conference with visiting German Chancellor Angela Merkel, Trump appeared to joke about the dispute by reviving a diplomatic flap from Obama's tenure.
"As far as wiretapping, I guess, by this past administration, at least we have something in common, perhaps," Trump said in response to a question as he stood beside Merkel.
In 2013, leaks from Edward Snowden disclosed that the National Security Agency, which conducts surveillance overseas, had eavesdropped on Merkel's cellphone as part of its efforts to spy on foreign leaders.
Obama later apologized to Merkel and said he had stopped the wiretapping. The two leaders ultimately repaired the rift, and their relationship was among the closest and most crucial Obama had with any world leader.
The House hearing Monday will be the first in Congress to publicly address the conclusions of the U.S. intelligence community that Russian spy agencies used cyberattacks and other tactics to interfere with the U.S. presidential race.
In a report released on Jan. 6, before Trump took office, the intelligence community assessed that Russian President Vladimir Putin had ordered the operation in an effort to hurt Democratic nominee Hillary Clinton and help Trump.
The report said hackers backed by Russian intelligence had stolen and leaked thousands of emails from Democratic National Committee computer systems. Some of the emails were embarrassing to Clinton's campaign.
Comey also is likely to face questioning about whether the FBI opened a formal investigation into contacts between the Trump campaign and Russian government officials — a question the FBI has so far been unwilling to answer in public.
Schiff said Sunday that "at the outset of the investigation, there was circumstantial evidence of collusion. There was direct evidence, I think, of deception."
His Republican counterpart, Rep. Devin Nunes (R-Tulare), chairman of the House Intelligence Committee, disagreed, saying on "Fox News Sunday" that he has seen "no evidence of collusion."
Ahead of the hearing Monday morning, Trump took to Twitter to say Democrats had "made up" claims that Russia was involved with the election.
Committee leaders have said classified and sensitive details about the FBI investigation will be discussed in a closed session.
Adm. Michael S. Rogers, director of the National Security Agency, will also testify.
Numerous Trump associates and campaign aides have had dealings with Russia, but no proof has emerged to indicate wrongdoing by the president or his associates.
Trump's first national security advisor, Michael Flynn, was forced to resign last month after leaks indicated he had discussed Obama administration sanctions on Russia during several phone conversations with Russian Ambassador Sergey Kislyak before Trump's inauguration and then had misled Vice President Pence about the conversations.
Atty. Gen. Jeff Sessions subsequently recused himself from the FBI investigations into Russia's role after news reports revealed he had twice met with Kislyak, including once in his Senate office in September, but had failed to disclose the meetings during his Senate confirmation hearing.
The question of whether Trump was the target of surveillance at times has veered into the surreal.
White House officials scrambled to explain themselves Friday, for example, after a raucous White House news briefing sparked a diplomatic flap with Britain, one of America's closest allies.
It began when Press Secretary Sean Spicer read a series of news stories to reporters on Thursday in an attempt to defend Trump's claim. One was an allegation from a Fox News commentator, Andrew Napolitano, that Obama had used British spies to avoid any "American fingerprints" on the surveillance.
Britain's Government Communications Headquarters, or GCHQ, the British equivalent of the NSA, issued a rare and angry denial.
"Recent allegations made by media commentator Judge Andrew Napolitano about GCHQ being asked to conduct 'wiretapping' against the then-president-elect are nonsense. They are utterly ridiculous and should be ignored," a GCHQ official told reporters.
A spokesman for Prime Minister Theresa May said senior British officials had protested to the White House.
"We've made clear to the U.S. administration that these claims are ridiculous and should be ignored. We've received assurances that these allegations won't be repeated," May's spokesman said.
For its part, Fox News issued a statement saying it "knows of no evidence of any kind" to support the claim that it had aired.
One House Republican called on Trump to apologize to Obama, repeating Intelligence Committee leaders' assertions that no evidence has surfaced to support Trump's claim.
"Frankly, unless you can produce some pretty compelling proof, then ... President Obama is owed an apology in that regard," said Rep. Tom Cole (R-Okla.). "Because if he didn't do it, we shouldn't be reckless in accusations that he did."
5:36 a.m.: This article was updated with additional material on President Trump's tweets.