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The bipartisan leaders of the House Intelligence Committee said Wednesday there is still no evidence Trump Tower was wiretapped ahead of the 2016 election, refuting the president’s explosive claims that President Barack Obama authorized surveillance of his campaign headquarters.

“To date, I’ve seen no evidence that supports the claim that President Trump made that his predecessor had wiretapped he and his associates at Trump Tower," the committee's ranking Democrat, Rep. Adam Schiff said. "Thus far, we have seen no basis for that whatsoever."

Schiff said he will ask FBI Director James Comey directly about the claims when he testifies March 20 as part of the committee’s investigation into Russian interference in last year’s presidential election.

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Trump tweeted earlier this month “Obama had my ‘wires tapped’ in Trump Tower just before the victory.” The claim, presented without evidence, was met with immediate skepticism from lawmakers questioning what the Republican meant.

A spokesman for Obama called the claim “simply false.”

“Are you going to take the tweets literally? And if you are, then clearly the president was wrong,” Chairman Devin Nunes told reporters.

The California Republican said questions remain over the "interpretation" of Trump's tweet and whether Trump associates were targeted by intelligence agencies. The committee heads sent a letter to intelligence officials asking for the names of U.S. citizens included in collection efforts as part of its inquiry into leaks. But the results may also shed light on whether communications from Trump Tower were captured as part a different intelligence gathering effort.

Former National Security Adviser Michael Flynn’s communications with the Russian ambassador to the U.S. after the election were gathered because of “incidental collection,” according to intelligence officials. Nunes said public reports of the phone call could be the result of “potential misuse.”

Republican Sen. Lindsey Graham said later Wednesday that the FBI informed his office it would comply with a bipartisan request to know into whether the bureau had requested a warrant to wiretap Trump Tower.

“We’re going to get an answer to whether or not the Trump campaign was ever surveilled,” he said during a hearing on Russia.

FBI Director James Comey was also on Capitol Hill Wednesday for a closed-door meeting with lawmakers about the investigation into Moscow.

Trump administration officials have struggled to explain the wiretapping claims. White House press secretary Sean Spicer said last week the tweet “speaks for itself,” later saying Trump meant the Obama administration authorized a broad range of surveillance against him during the campaign.

“The reality is I don’t think they have the foggiest idea what was behind the President’s claim except maybe something he watched on TV. I think the rest is designed to downplay, minimize or obfuscate the fact that the president said something that was patently untrue. But that is my interpretation,” Schiff said.