"There was no evidence whatsoever, at the time, of collusion between the Trump campaign and the Russians," Clapper, a retired three-star general and career intelligence officer, told ABC News' Brian Ross in an interview Monday for "World News Tonight."
Clapper said in the interview, "There was no wiretap against Trump Tower during the campaign conducted by any part of the national intelligence community."
"None at all ... including the FBI," he said.
FBI Director James Comey asked the Department of Justice — his supervisor — to publicly refute Trump's claim, a senior official told ABC News. Comey felt Trump's allegation impugned the FBI's reputation by suggesting agents conducted illegal or politically motivated surveillance.
Clapper wasn't asked by the Trump White House to do what Comey declined to do — throw it a political lifeline. But in the interview Clapper disputed claims about Russian infiltration of the Trump campaign anyway, with the encouragement of the FBI's leadership, current and former U.S. officials told ABC News.
They said Clapper, who served presidents of both parties in uniform and as a civilian director of national intelligence under Obama, wanted to set the record straight on the wiretapping claim and on the suggestion by Trump critics that the Kremlin may have succeeded in recruiting someone in Trump's camp.
"I'm led to conclude this really just didn't happen," said Hayden, the author of the new book "Playing to the Edge: American Intelligence in the Age of Terror."
Clapper, asked about the White House's declining to accept the wiretapping denials by him and by Comey (through surrogates), said on Monday that he was not surprised, adding of Trump, "Well, that's his prerogative."
"I think when he says things, which he for whatever reason believes, he is — it's been my observation — he doesn't back down from it," Clapper told ABC News.
One former senior Trump campaign aide told ABC News today that no one in his administration contacted former campaign aides to even ask if they met with Russian officials before he and his spokespeople made numerous public denials this year that no one from the campaign had met with any Russians.
"They're winging it, just like they did during the campaign," the former campaign aide said.
Most notably, last week Attorney General Jeff Sessions acknowledged he had two meetings with Kislyak, despite testifying at his recent Senate confirmation hearing that he had no meetings with the Russian government while advising the Trump presidential campaign last year. Democratic leaders have called for Sessions to resign; instead, he recused himself from overseeing any Department of Justice investigations of Russian attempts to influence the election.
ABC News reported earlier this week that Clapper declined Trump's Jan. 11 request that he publicly refute a dossier of salacious allegations about Trump and his campaign aides compiled by a former British government spy for a Washington political intelligence firm. Clapper's reason for declining was that the report's sources and allegations couldn't be corroborated or even properly investigated.
"[Trump] informed me directly that he believed all the information that was contained in the data of this dossier was false," Clapper said.
Asked what parts of the dossier had been corroborated by other sources, Clapper said that the intelligence community was able to confirm that Putin hated former President Bill Clinton and former Secretary of State Hillary Clinton. Clapper refused to comment further on the dossier.
Putin's "rabid animus," as Clapper called it, appears to stem from lingering Russian anger over the Clinton administration's use of military power in the late 1990s to defend Bosnian Muslims from Serbs aligned with Russia, one analyst said.