WASHINGTON -- President Trump had more sharp words today about the FBI's use of an informant within his campaign as it investigated Russian meddling. And the secretary of the Department of Homeland Security made some surprising remarks about the investigation.

The president declined Tuesday to express confidence in his Deputy Attorney General Rod Rosenstein a day after meeting with him to discuss allegations of FBI misconduct during the 2016 election.

Speaking in the Oval Office, Mr. Trump responded to the news that an FBI informant was in contact with members of his campaign.

"That would be one of the biggest insults that anyone's ever seen," Mr. Trump said. "If they had spies in my campaign, during my campaign for political purposes, that would be unprecedented in the history of our country."

During the 2016 election, the informant met with at least three Trump campaign advisers after the FBI learned they had suspicious contacts with Russians.

Former Director of National Intelligence James Clapper defended using an informant on ABC's "The View."

"Was the FBI spying on the Trump campaign?" co-host Joy Behar asked.

"No. They were not," Clapper responded.

"They were spying on -- a term I don't particularly like -- but on what the Russians were doing," Clapper said. "Trying to understand were the Russians infiltrating, trying to gain access, trying to gain leverage and influence."

While the president fumed over surveillance, Homeland Security Secretary Kirstjen Nielsen stunned some lawmakers by saying she wasn't aware of the U.S. intelligence assessment that Russia's meddling was intended to help Mr. Trump get elected.

"I do not believe that I have seen that conclusion ... That the specific intent was to help President Trump win," Nielsen said. "I am not aware of that, but I do generally have no reason to doubt any intelligence assessment."

The DHS tried to walk back Nielsen's comments -- insisting she has read the intelligence assessment and is aware of the threat posed by Russia.