"I never worked for Russia and you know that answer better than anybody," Trump told reporters as he was leaving the White House for a trip to New Orleans. "Not only did I never work for Russia, I think it's a disgrace that you even asked that question because it's a whole big fat hoax," Trump said.
The New York Times first reported the story, including details about how officials were concerned about the president's behavior before and after he fired Comey. The purpose of the FBI's counterintelligence program, as defined by the agency itself, is to neutralize national security threats from foreign intelligence services and in the past, countering Russian efforts has been its primary mission.
Trump has long battled allegations of ties to Russia, the focus of special counsel Robert Mueller's investigation into possible collusion between Russia and the Trump campaign during the 2016 election.
About the same time as Trump was talking Monday morning, former Democratic presidential candidate Hillary Clinton re-tweeted a video of herself from her final presidential debates with Trump, in which she calls Trump a "puppet" for Russian President Vladimir Putin and he interrupts, "No puppet, no puppet -- you're the puppet."
"Like I said: A puppet," Clinton said Monday.
Trump went after the FBI Monday, attempting to cast the bureau and the alleged counterintelligence investigation as "dirty" and his move to fire Comey as "a great thing [he] did for [the] country."
"The people doing that investigation were people that have been caught, that are known scoundrels there, I guess you could say are dirty cops," Trump said, mentioning fired deputy director Andrew McCabe and former FBI officials Lisa Page and Peter Strzok.
"Let me tell you something, when people see that, you have an angry country. Because the whole thing is a hoax. It is a big hoax and it is very bad for our country," Trump said.
John Cohen, former acting undersecretary for Intelligence and Analysis at the Department of Homeland Security and an ABC News contributor, said there would be multiple levels of review to ensure an investigation like this was warranted before it would've been opened.
"While the president seeks to paint this as a politically motivated action by a few rogue agents, that's just not how it works," Cohen said.
Opening a counterintelligence investigation specifically looking at the president would be an "extraordinarily serious undertaking," Cohen said, and wouldn't have been done without senior career officials' approval.
"There are too many safeguards within the Justice Department to allow it to be done for political purposes," Cohen said. "The only way it would be opened on the President of the United States is if it was reviewed at the highest levels."
While it remains to be seen what the results of the reported investigation would be, or whether it's still ongoing, the former DHS official said counterintelligence investigations are not meant to be concluded quickly, but meant to provide the U.S. intelligence community with the maximum amount of information on how the foreign actor is operating and use that information for the agency's own goals. They often go on for years without any type of action, Cohen said.
"It remains to be seen what the results of the investigation are, but with that said -- this is highly unusual and we are in uncharted and very dangerous waters," Cohen said.
The first time Trump was publicly asked about the report -- and whether he currently or ever had worked for Russia -- on Saturday night by Fox News by host Jeanine Pirro, Trump denounced the story as "the most insulting" ever written about him but didn't directly answer the question.
Adding to questions about his relationship with Russia, the president was also asked on the White House South Lawn about Washington Post reporting over the weekend that said the president went to great lengths to conceal the details of several of his meetings with Putin, including on one occasion taking possession of the notes made by an American interpreter, the sole attendee other than Trump and the Russian president.
Trump wouldn't say whether he intended to hand over the notes, which House Democrats are considering subpoenaing.
"It is a lot of fake news. It was a very good meeting. It was a very successful meeting. I have those meetings with everybody. I just know nothing about it. It was a very, very successful meeting," Trump said.