Sen. Richard Blumenthal (D-Conn.) said Monday he would not allow President Trump's “bullying” to distract him after coming under repeated Twitter fire from the commander-in-chief.

“There is an ongoing special counsel investigation. It is real. It is based on fact," Blumenthal told CNN’s “The Situation Room” Monday evening, referring to the probe into Russia's involvement in last year's election.

"That’s what is important. That focus is what really matters. Our national security and rule of law is at risk. And that’s where our focus should be. It is not about me,” he said.

Blumenthal’s appearance came minutes after Trump ripped him for a second time on Monday, saying the senator “should take a nice long vacation in Vietnam.”

Trump has mocked Blumenthal over a past controversy; the senator came under criticism in 2010 for statements saying that he had served in Vietnam. His service was in the Marine Reserve and he did not go to Vietnam. Blumenthal later said he regretted referring to his service in Vietnam, instead of his service during Vietnam.

CNN host Wolf Blitzer pressed Blumethal, asking if there is some sort of personal issue between him and Trump. The senator is married to the daughter of a wealthy New York real estate developer.

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“I have no idea about what is in his mind. What I do know is I will not be distracted by this bullying,” Blumenthal said. “And these bullying tweets reinforce for me the need for a piece of legislation that I am helping to lead with [North Carolina GOP Sen.] Thom Tillis Thomas (Thom) Roland TillisWhat Senate Republicans have said about election-year Supreme Court vacancies Chamber of Commerce endorses McSally for reelection Airline job cuts loom in battleground states MORE and others, bipartisan coalition, to prevent firing of the special counsel, Robert Mueller.”

Trump began Monday with early-morning tweets about Blumenthal.

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

"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. Now he judges collusion?"

The president’s tweets followed Blumenthal’s appearance on CNN’s “New Day,” where he expressed a fear that the Justice Department is "weaponizing" laws after declaring a crackdown on leaks.

Blitzer asked Blumenthal if he wanted to say anything, including about his military service, to the president during his on-air interview.

“All I would say is let’s protect the independence and integrity of the special counsel who is investigating Russian interference in our 2016 election, possible collusion and conspiracy involving the Trump campaign, and allegations of obstruction of justice afterwards,” Blumenthal said.