President Donald Trump has suffered a blow to his credibility because of his false statements about being wiretapped, but he is attempting to change the subject and urging core supporters to rally behind him while he is under siege.

FBI Director James Comey damaged Trump's credibility Monday by discrediting the president's unsubstantiated claims on Twitter that former President Barack Obama ordered a wiretap of Trump Tower in New York during the 2016 presidential campaign. "I have no information that supports those tweets, and we have looked carefully inside the FBI," Comey told the House intelligence Committee. He said the Justice Department has no evidence supporting Trump's charges either.

Comey also told the committee that the FBI is investigating whether members of Trump's campaign colluded with Russia to influence the 2016 election and defeat Democratic presidential nominee Hillary Clinton. Trump had insisted on Twitter, as recently as early Monday morning prior to Comey's testimony, that the possibility of collusion is "fake news" generated by his political adversaries to damage his presidency.

Trump said the real issue is the leaking of classified information designed to hurt Trump, not any possible wrongdoing by him or his supporters which he denies. But the reality of the FBI investigation means the issue of possible collusion will hang over Trump for the foreseeable future.

Trump and congressional Republicans are attempting to shift attention from his credibility problems to the issue of leaks from anonymous government officials to the news media. Rep. Devin Nunes, R-Calif., chairman of the Intelligence Committee, said, "We aim to determine who has leaked or facilitated leaks of classified information [about contacts with Russia and other matters] so that these individuals can be brought to justice."

The New York Times has reported that U.S. intelligence officials concluded in January that Russian President Vladimir Putin ordered a covert campaign to damage Hillary Clinton's campaign and assist Trump. The effort included hacking the Democratic National Committee and releasing emails that embarrassed the Clinton campaign and the Democrats.

Comey acknowledged that the FBI is "investigating the nature of any links between individuals associated with the Trump campaign and the Russian government, and whether there was any coordination between the campaign and Russia's efforts."

Trump's apparently baseless charges against Obama have caused a political sensation and generated intense criticism. At 6:35 a.m. on March 4, Trump wrote on Twitter, "Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower [his residence and campaign headquarters] just before the victory. Nothing found. This is McCarthyism!"

Trump's comment referred to the unfounded accusations and investigations by Wisconsin Sen. Joe McCarthy's to root out alleged communists from the government during the 1950s. Trump also wrote on Twitter March 4, "How low has President Obama gone to tapp [sic] my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!"

Monday's developments in the Intelligence Committee undermined Trump's believability for many. Leon Panetta, former White House chief of staff for President Bill Clinton and former defense secretary and director of central intelligence under President Barack Obama, told CNN that Trump was "irresponsible" to tweet without making sure he had the facts. Trump is not a teenager throwing a tantrum, Panetta said; he is the president of the United States and he is "impacting his credibility as president."

Jennifer Palmieri, communications director for Clinton's 2016 presidential campaign, told the Washington Post that the Comey statements were "a brutal blow to his credibility and a huge opportunity cost. He should be focused on salvaging his health-care bill, not continuing to draw all of America's eyes to the Russia investigation."

Rep. Peter King, R-N.Y., a member of the Intelligence Committee, told the New York Times, "The tweets make it much more difficult for us as we try to build a case against these leakers. We always have to be answering questions about the tweets--it puts us on defense all the time when we could be building a case for the president."

For his part, Trump appeared at a rally for himself Monday night in Louisville, Kentucky, where he attempted to energize his supporters. He ignored the story of his false wiretap allegation against Obama and praised himself for attempting to fulfill his campaign promises to build a wall between the United States and Mexico and to eventually lower taxes.