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FBI Director James Comey dealt President Donald Trump a stinging rebuke on Monday at a time of acute political vulnerability for the White House.

In his opening statement before the House Intelligence Committee, Comey confirmed that the FBI is investigating Russia's interference in the presidential election, and whether any of Trump's associates collaborated with Vladimir Putin's government.

On another day, in another time, that would be the bombshell. But Comey said more, establishing that the president's charge his predecessor had wiretapped him was false. Working systematically, tweet by explosive tweet, under questioning from lawmakers Comey repeatedly insisted there was "no evidence" to substantiate Trump's March 4 claims.

Nothing to prove Barack Obama had ordered phones tapped at Trump Tower. Nothing to indicate Obama had somehow subverted Nixon-era safeguards enacted to prevent abuses of power and protect Americans from top-secret foreign electronic surveillance programs. No reason to conclude Obama had violated the rules of a decades-old intelligence alliance and solicited a foreign ally to carry out the spying.

"I'm not going to try and characterize the tweets themselves," Comey said. "All I can tell you is we have no information that supports them."

Taken in sum, the same FBI director who boosted Trump's political fortunes in the closing days of the presidential campaign by acknowledging his agency had reopened an investigation into rival Hillary Clinton's use of private email dealt the president one of the worst political blows of his young administration. The damage comes at perhaps the worst possible time.

Comey's testimony opened a crucial week for the White House. Senators have begun weighing the nomination of Neil Gorsuch to the Supreme Court and members of the House are set to vote on Trump's preferred plan to repeal and replace Obamacare. That vote is certain to be close, and vulnerable House Republicans already skittish about a plan that manages to both institutionalize government involvement in the health-care industry while also risking the coverage of their constituents are certain to be taking stock of Trump's political capital.

The president was already staggering into the week before Comey began speaking.

A Gallup poll released Sunday showed his approval rating at 37 percent — down 8 percentage points from a week earlier, and lower than Obama's at any point in his presidency.

A Congressional Budget Office review found that under the health-care plan Trump's endorsed, 24 million Americans would lose their coverage over the next decade. A federal court again struck down Trump's attempt to block travel from six majority-Muslim countries. And a frosty visit with German Chancellor Angela Merkel, coupled with a high-profile spat with the U.K. after the White House highlighted a Fox News commentator's charge a British intelligence agency may have assisted Obama in spying on Trump, only deepened concerns about the president's competence on the world stage.

But the White House and congressional Republicans have reason not to panic, yet.

For one, Gorsuch seems likely to be confirmed, barring a dramatic misstep in his confirmation hearing. That will provide the president a political win and buoy conservatives who expected deceased Justice Antonin Scalia to be replaced with a jurist of a similar ilk.

And while Comey's testimony is certain to give fodder to Trump's critics, White House aides were ebullient after House Intelligence Committee Chairman Devin Nunes, a California Republican, said his panel hadn't seen evidence to indicate collusion between the Russian government and the Trump campaign.

White House press secretary Sean Spicer highlighted that former acting CIA chief Michael Morrell and former director of national intelligence James Clapper have both backed Nunes, saying they had seen no evidence of Trump and the Russians working together.

A White House official who refused to be identified noted Morrell's and Clapper's remarks and said the administration takes them at their word. There's no evidence of a Trump-Russia collusion, the official said in a statement.

The president tweeted ahead of Comey's testimony that allegations he's tied to the Russians are "FAKE NEWS and everyone knows it!"

"The Democrats made up and pushed the Russian story as an excuse for running a terrible campaign," he continued.

The president's allies on Capitol Hill used their time with the FBI director to focus attention on government leaks about contacts between Russian officials and Trump allies. That has the dual benefit of depicting the investigation into Russia as a partisan campaign to undermine the president, while discouraging more of the leaks that have plagued the early weeks of the Trump administration.

Trey Gowdy, the South Carolina Republican who had led the House Benghazi inquiry, used much of his time with Comey to ask the FBI director if he was investigating who shared details of former National Security Adviser Michael Flynn's conversations with Russian Ambassador to the U.S. Sergey Kislyak with the media.

Flynn was forced to resign after it was found he had misled senior administration officials, including Vice President Mike Pence, about his discussions with Kislyak. Comey wouldn't say if the FBI was trying to track down the leaks, explaining that he did not want to validate or debunk media accounts.

"The real story that Congress, the FBI and all others should be looking into is the leaking of Classified information," Trump tweeted early Monday. "Must find leaker now!"

A number of Trump aides tweeted a clip from the hearing of Comey acknowledging leaks had become "unusually active" in recent months.

But while some Republicans on the committee suggested Clinton's campaign may have collaborated with Russians, Comey bluntly rejected that notion. He said Putin's goal was to undermine the former secretary of state's candidacy while aiding Trump's, as U.S. intelligence agencies concluded in January.

"They wanted to hurt our democracy, hurt her and help him," Comey said. "Putin hated Secretary Clinton so much that the flip side of that coin was that he had a clear preference for the person running against the person he hated so much."