(CNN) —  

A freshman Democratic member of Congress on Thursday stood by her accusation that Republican Sen. Lindsey Graham has been “compromised,” citing his staunch defense of President Donald Trump, adding that he can “no longer stand up for the truth.”

But when pressed in a CNN interview, the congresswoman, Rep. Ilhan Omar of Minnesota, was unable to provide evidence for her claim, chalking it up to an opinion based on her observations.

Omar first made the accusation on Twitter on Tuesday when she shared a video of a 2015 CNN interview of Graham, then a GOP presidential candidate, criticizing Trump, whom he calls a “race-baiting, xenophobic, religious bigot” in the interview.

“They got to him, he is compromised!” Omar tweeted of Graham, who has since become one of Trump’s strongest allies in the Senate since his former rival took office.

Asked about the tweet on Thursday by CNN’s Poppy Harlow and Jim Sciutto on “Newsroom,” Omar doubled down on her accusation.

“So over the last three years, we have seen many times where Sen. Lindsey Graham has told us how dangerous this President could be if he was given the opportunity to be in the White House. And all of the sudden, he’s made not only a 180 turnaround, but a 360 turnaround. And so I am pretty sure that there is something happening with him,” Omar said, suggesting Graham’s support could have to do with campaign funding for the senator or polling numbers in his district.

“He is somehow compromised to no longer stand up for the truth and to make sure that he is fighting to protect the oath that he took in serving the American people,” she said.

Omar added, “the evidence really is present to us. It’s being presented to us in the way that he is behaving.”

A spokesman for Graham declined to comment on Omar’s comments Thursday.

When Harlow asked Omar about specific evidence to back up her claims, the congresswoman explained that her tweet “was just an opinion based on what I believe to be visible to me – and I’m pretty sure there are lots of Americans who agree on this.”

Graham, who faces re-election in 2020, has aligned himself with many of Trump’s positions, though he still occasionally calls out the President. Following an attack by ISIS in Syria on Wednesday that killed four Americans, Graham sharply criticized Trump for his decision last month to withdraw US troops from the country, saying that recent statements by the President have “set in motion enthusiasm by the enemy we’re fighting.”