At last week’s fiery hearing probing sexual assault allegations against Judge Brett Kavanaugh, Democratic Sen. Richard Blumenthal lectured the Supreme Court nominee on the implications of telling even a single lie.

“Falsus in uno, falsus in omnibus,” Blumenthal, D-Conn., told Kavanaugh, reciting a Latin phrase. “It means 'False in one thing, false in everything.'”

But Blumenthal’s own difficult history with the truth is coming back to haunt him amid the Kavanaugh fight, with President Trump and Republican senators slamming him for inflating his military service during the Vietnam War.

In the 2000s, when Blumenthal served as Connecticut’s attorney general, he began to claim that he served in the Vietnam War. Blumenthal, repeatedly, has touted his experience during the war.

“When we returned [from Vietnam], we saw nothing like this,” Blumenthal reportedly said in 2003.

“We have learned something important since the days I served in Vietnam,” The New York Times quoted Blumenthal as saying in 2008.

“I served during the Vietnam era,” Blumenthal reportedly said at a Vietnam War memorial in 2008. “I remember the taunts, the insults, sometimes even the physical abuse.”

But Blumenthal didn’t serve in Vietnam. He reportedly obtained at least five military deferments between 1965 and 1970. He eventually served in the U.S. Marine Corps Reserve, but did not deploy to Vietnam.

In the wake of Blumenthal questioning Kavanaugh -- who faces multiple sexual assault or misconduct allegations, which he denies -- Trump and fellow Republicans have not let him forget his own past statements.

“You have the great Vietnam War hero—who didn’t go to Vietnam—[Sen. Richard] Blumenthal,” Trump said at a rally Monday evening. “How about Blumenthal? We call him ‘Da Nang Blumenthal.”

Blumenthal, last week, said Trump’s initial reluctance to demand a FBI supplemental background probe of Kavanaugh was “tantamount to a cover-up.” Blumenthal hit Kavanaugh during the hearing on questions related to his high school yearbook entries, calendar entries and drinking habits.

“For 15 years as the attorney general of Connecticut, he went around telling war stories,” Trump said. “’People dying left and right—but my platoon marched forward!’ He was never in Vietnam. It was a lie. And then he’s up there saying, ‘We want the truth from Judge Kavanaugh.’ And you’re getting the truth from Judge Kavanaugh.”

During the Kavanaugh hearing, Blumenthal said “the core of why we are here today really is credibility.”

Kavanaugh is accused of sexually assaulting Dr. Christine Blasey Ford while at a high school party 36 years ago. Ford, who also testified before the Senate Judiciary Committee last week, alleged Kavanaugh pinned her down and tried to remove her clothes. Her attorney says Ford believes this to have been an “attempted rape.”

Kavanaugh also faces allegations from Deborah Ramirez, who claims that while freshmen at Yale University, the Supreme Court nominee exposed himself to her at a dorm party in the 1980s; and Julie Swetnick, who is represented by Stormy Daniels’ attorney Michael Avenatti and claims that Kavanaugh was involved in or present at “gang” and “train” rapes in the 1980s.

Kavanaugh has vehemently denied the allegations.

Amid the hearing, though, Sen. Tom Cotton, R-Ark., an Iraq and Afghanistan war veteran, hit Blumenthal for his credibility.

“.@SenBlumenthal lied for years about serving in Vietnam, which is all you need to know about his courage & honesty. Maybe he should reconsider before questioning Judge Kavanaugh’s credibility,” Cotton tweeted.

Blumenthal’s office did not immediately respond to Fox News’ request for comment.

In 2010, Blumenthal admitted to giving misleading statements about his service.

“On a few occasions I have misspoken about my service,” Blumenthal, as quoted by The New York Times, said, adding that he served in the U.S. Marine Corps Reserve. “And I regret that and I take full responsibility. But I will not allow anyone to take a few misplaced words and impugn my record of service to our country.”

Fox News’ Gregg Re contributed to this report.