George Santos is a “sociopath” who thrives on negative attention, another New York Republican congressman said.

“He’s a sociopath,” Nick LaLota told CNN on Wednesday, after Santos’s confrontation with Mitt Romney at Joe Biden’s State of the Union address made headlines the night before.

“He looks for that attention. Even the negative attention drives him. It’s become an embarrassment and a distraction to the Republicans in the House.

“And every time I have to come to something like this and talk about George Santos, I can’t talk about what Republicans ought to be doing instead.”

Santos later told reporters Romney’s remarks were “reprehensible” and said the senator’s behaviour “wasn’t very Mormon”.

Romney, a senator from Utah, is a member of the Church of the Latter-Day Saints. Santos claimed to have Jewish grandparents who escaped the Holocaust, a lie repeatedly exposed.

The Merriam-Webster dictionary defines “sociopathic” as “of, relating to, or characterised by asocial or antisocial behavior or exhibiting antisocial personality disorder”.

LaLota was elected to Congress in New York’s first district last November, while Santos won in the third.

Since then, Santos’s résumé has been shown to be largely made-up, his often bizarre past behaviour exposed and his campaign finance filings investigated.

The congressman is also the subject of allegations of criminal behaviour, including a sexual harassment claim leveled by a former congressional aide.

The 34-year-old has admitted embellishing his résumé but denied wrongdoing and repeatedly said he will not resign.

LaLota is among a growing number of Republicans, Democrats and constituents who have called on Santos to quit. Party leaders accepted Santos’s withdrawal from committee assignments but have not said he should resign.

Santos supported the House speaker, Kevin McCarthy, through 15 rounds of voting for the position, against a far-right rebellion.

Members of Congress often resign amid scandal but very few are reprimanded, censured or expelled. The last of only five members ever expelled was James Traficant Jr, an Ohio Democrat removed in 2002 after being convicted of crimes including obstruction of justice and racketeering.

On Tuesday night, ahead of Biden’s speech, Santos positioned himself near the centre aisle of the House chamber as senators entered.

He was seen to exchange words with Romney, the 2012 Republican presidential nominee who is now a senator from Utah.

Romney later told a scrum of reporters: “I didn’t expect that he’d be standing there trying to shake hands with every senator and the president of the United States.

“Given the fact that he’s under ethics investigation, he should be sitting in the back row and staying quiet instead of parading in front of the president and people coming into the room.”

Romney called Santos a “sick puppy” and said he told the New Yorker he “shouldn’t be in Congress … if he had any shame at all, he wouldn’t be there”.

Asked if he was disappointed McCarthy had not called on Santos to resign, Romney said: “Yes.”

Romney said he didn’t hear what Santos said to him. Santos claimed Romney told him he was an “ass” and to have retorted that the senator was “a much bigger asshole”. He also taunted Romney, tweeting “a reminder that you will NEVER BE PRESIDENT!”

On Wednesday, Santos told reporters: “It’s not the first time in history that I’ve been told to shut up and go to the back of the room, especially by people who come from a privileged background.

“I’m never gonna shut up and go to the back of the room. I think it’s reprehensible the senator would say such a thing to me … it wasn’t very Mormon of him.”

LaLota told CNN: “Mitt Romney is right on this one. I’ve been clear on George Santos for months now. He does not deserve to be in Congress. He’s all about the rhetoric, he’s all about the drama, and he’s fallen far below the standard that we all should hold ourselves to.”