President Trump on Monday launched a renewed attack on Sen. Richard Blumenthal (D-Conn.), calling him “a phony Vietnam con artist” on Twitter after the senator appeared on television.

Trump’s tweets came after Blumenthal voiced support on CNN for continuing the investigation into Russian meddling in last year's election and expressed concern about the Justice Department’s increased focus on rooting out administration officials who leak information damaging to Trump.

[Trump says his political base is ‘stronger than ever’ despite polling to the contrary]

“Politicizing the Department of Justice for personal ends, I think, is a disservice to the law, and it’s also potentially a violation of the spirit of the First Amendment,” Blumenthal said, suggesting that the department was “weaponizing” laws against leaking sensitive information.

“Never in U.S.history has anyone lied or defrauded voters like Senator Richard Blumenthal,” Trump wrote on Twitter shortly afterward. “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.”

Interesting to watch Senator Richard Blumenthal of Connecticut talking about hoax Russian collusion when he was a phony Vietnam con artist! — Donald J. Trump (@realDonaldTrump) August 7, 2017

Never in U.S.history has anyone lied or defrauded voters like Senator Richard Blumenthal. He told stories about his Vietnam battles and.... — Donald J. Trump (@realDonaldTrump) August 7, 2017

...conquests, how brave he was, and it was all a lie. He cried like a baby and begged for forgiveness like a child. Now he judges collusion? — Donald J. Trump (@realDonaldTrump) August 7, 2017

Trump was referencing a 2010 controversy over Blumenthal’s military service. During his Senate campaign, Blumenthal came under sharp criticism for repeated remarks over the years that he had “served” in Vietnam, even though he did his full Marine service in the United States.

Blumenthal was granted several deferments between 1965 and 1970 and then joined the Marine Corps Reserve but did not serve in Vietnam. He later said he misspoke and intended to say that he was in the Marine Reserve during the Vietnam conflict.

Blumenthal responded to Trump on Twitter later Monday morning, writing, “Mr. President: Your bullying hasn't worked before and it won't work now. No one is above the law.”

Mr. President: Your bullying hasn't worked before and it won't work now. No one is above the law. — Richard Blumenthal (@SenBlumenthal) August 7, 2017

In an interview later Monday on CNN, Blumenthal said Trump's tweets reinforce the need for legislation he is pushing that would prevent the president from firing Robert S. Mueller III, the special counsel looking into allegations of Russian meddling in the election and possible collusion with the Trump campaign.

Trump's tweets appeared to overstate what had happened with Blumenthal. NBC News said its analysis found no evidence that Blumenthal had bragged about his Vietnam battles nor that he had cried about the controversy during his 2010 campaign:

“No and no,” a Blumenthal spokesman told NBC on Monday when asked whether the senator had bragged or cried.

Trump returned to the issue later Monday, offering a suggestion to Blumenthal in an afternoon tweet: “I think Senator Bluementhal should take a nice long vacation in Vietnam, where he lied about his service, so he can at least say he was there.”

Trump has attacked Blumenthal on the same issue on past occasions.

In February, Trump pointed to the episode in trying to undermine Blumenthal’s credibility after he publicly shared that Trump’s then-Supreme Court nominee, Neil M. Gorsuch, had told him that he found Trump’s attacks on the federal judiciary “disheartening” and “demoralizing.” Gorsuch later acknowledged having those concerns.

In May, Trump went after Blumenthal when the senator criticized the president during television appearances for his firing of then-FBI Director James B. Comey.

“Watching Senator Richard Blumenthal speak of Comey is a joke,” Trump said in one of those tweets.

The president’s tweets on Monday came during what aides are describing as a 17-day “working vacation” at his golf club in Bedminster, N.J. In earlier tweets, Trump stated that his political base is stronger than ever, despite recent polling to the contrary.

In recent days, his aides have touted a greater discipline brought to the White House by retired Marine Corps Gen. John F. Kelly, Trump’s new chief of staff. Since the arrival of Kelly, who joined Trump in Bedminster over the weekend, the president has continued to be active on Twitter.