President Trump on Monday called Sen. Richard Blumenthal, D-Conn., a "con artist" just moments after Blumenthal said he's worried that Trump is trying to "politicize" the Justice Department.

"Interesting to watch Senator Richard Blumenthal of Connecticut talking about hoax Russian collusion when he was a phony Vietnam con artist!" Trump tweeted.

"Never in U.S. history has anyone lied or defrauded voters like Senator Richard Blumenthal," Trump tweeted later. "He told stories about his Vietnam battles and conquests, how brave he was, and it was all a lie."

"He cried like a baby and begged for forgiveness like a child," Trump added. "Now he judges collusion?"

Blumenthal a decade ago claimed several times in public that he served in Vietnam, but he never did. Instead, he got five military deferments that let him skip out the war, according to the New York Times.

After Blumenthal criticized Trump in May, Trump said Blumenthal is the one who should be investigated.

On CNN Monday, Blumenthal said he's worried that the Justice Department's Friday announcement that it is reviewing subpoena policies for reporters as a bad sign. Blumenthal said U.S. officials who leak information should be prosecuted, but said the government shouldn't go after reporters.

"I'm very concerned that the Department of Justice is weaponizing these laws for its personal and political ends, and specifically for the White House's purposes," he said.

"That's a chilling effect on the press and on whistleblowers, and on information that doesn't involve classified data or disclosures, but in fact maybe just embarrassing or unwelcome," he added.

Blumenthal said without the free press, much less would be known about the Trump transition team's meetings with Russian officials.