Former Speaker Newt Gingrich (R-Ga.), a longtime supporter of President TrumpDonald John TrumpTrump nominates ambassador to Turkey Trump heads to Mar-a-Lago after signing bill to avert shutdown CNN, MSNBC to air ad turned down by Fox over Nazi imagery MORE, declared on Monday that Trump's performance at a news conference with Russian President Vladimir Putin was "the most serious mistake of his presidency."

The comments from the former Speaker came after the U.S. president challenged his own intelligence community's conclusion that Moscow interfered in the 2016 election during a joint news conference with Putin.

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"They said they think it’s Russia. I have President Putin — he just said it’s not Russia," Trump said, adding that he does not "see any reason why it would be" Russia.

Trump has repeatedly criticized the special counsel investigation into possible collusion between his campaign and Russia. But his remarks on Monday were an extraordinary break from his own administration, which last week indicted 12 Russian officials on charges of hacking Democratic servers in 2016.

The president's comments prompted criticism from both sides of the aisle and a statement from Director of National Intelligence Dan CoatsDaniel (Dan) Ray CoatsEx-Trump official says intel community's testimony interfered in US-North Korea talks Is a presidential appointment worth the risk? Intel agencies' threat assessment matters more than tiff with Trump MORE standing by the intelligence community's determination that Russia interfered in the 2016 election.

"We have been clear in our assessments of Russian meddling in the 2016 election and their ongoing, pervasive efforts to undermine our democracy, and we will continue to provide unvarnished and objective intelligence in support of our national security," Coats said.