US President Donald Trump boards Air Force One prior to departure from Joint Base Andrews in Maryland, February 25, 2019, as he travels to Hanoi, Vietnam for a second summit with North Korean leader Kim Jong Un.

President Donald Trump, in Vietnam, unleashed another Twitter tirade against Sen. Richard Blumenthal on Wednesday, ridiculing the Connecticut Democrat for his military record during the Vietnam War.

"I have now spent more time in Vietnam than Da Nang Dick Blumenthal, the third rate Senator from Connecticut (how is Connecticut is doing?). His war stories of his heroism in Vietnam were a total fraud — he was never even there," tweeted Trump, who received five draft deferments between 1964 and 1972.

"We talked about it today with Vietnamese leaders!"

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The president arrived in Hanoi, Vietnam late Tuesday, ahead of a meeting with North Korean leader Kim Jong Un on Wednesday.

Shortly before the second U.S.-North Korea summit in less than a year, Trump met with the Vietnamese prime minister and other officials. He has described the Southeast Asian country as "thriving like few places on Earth."

"We generally decline to waste time engaging with Trump's brazen lies about Senator Blumenthal. Nothing new here," Maria McElwain, a spokesperson for Blumenthal, said when contacted by CNBC on Wednesday.

"But the American people should be concerned about the President of the United States squandering time and energy during sensitive negotiations with a serious nuclear threat peddling falsehoods about a political critic."