A US Navy veteran has accused the Republican congressman George Santos of refusing to hand over $3,000 raised in an online campaign to fund lifesaving surgery for his therapy dog.
Richard Osthoff, who spent six years in the Navy, said a charity group linked to Mr Santos created a GoFundMe page for his dog, Sapphire, but never gave him the money.
It comes after weeks of allegations that the New York congressman lied about several aspects of his life during his campaign for a seat in the US House of Representatives last year.
Mr Osthoff said he believes his dog's life would have been saved if he had access to the $3,000 (£2,431) donation pot.
"I was so livid that I realised that this guy is now a serving congressman," Mr Osthoff said.
"He doesn't deserve that job. It's horrendous that he could lie and steal and cheat his way through life.
"And now he's somebody that we're supposed to trust. It's disgusting. It's horrible. [He] should be ashamed of himself, but he doesn't ... He's a psychopath."
Mr Santos, 34, told US news outlet Semafor that the allegations were "fake" and that he had "no clue who this is".
Mr Osthoff received Sapphire, a pit bull, in 2005 from a rescue organisation to help him cope with his bipolar and post-traumatic stress disorder.
"I was going through some really bad times when I got out of the service," he said.
"My dad even told me at one point he thought I had a death wish."
By 2016, Sapphire was suffering from a cyst on her rib cage that "got to the size of maybe two grapefruits" over a few months.
Mr Osthoff, who was homeless at the time, could not afford the $3,000 it was estimated Sapphire's surgery would cost.
He was then referred to Mr Santos's charity - Friends of Pets United - by a vet technician, and the charity made a GoFundMe page for Sapphire.
"Everything had to be done through his [Mr Santos's] vets and his technicians and all that stuff at that point," Mr Osthoff said, adding that when he suggested going a different route, Mr Santos began "coming up with all these excuses" about the money.
"I knew there was something up. I knew it was fishy. And he started telling me that if the dog wasn't able to be worked on, the funds weren't going to go to me anyway. They were going to go to another animal that needed it," Mr Osthoff said.
"I told him, I was like: 'Look, I know what's going on here. You're mining my dog and my friends and my family for funds, and you're putting them in your own pocket'."
Mr Osthoff never received the money and said he was forced "to panhandle" to pay for her to be euthanised and cremated.
"It's [Santos's] fault that she passed as early as she did," he added.
Mr Santos has been accused of lying about his education and job history in recent weeks.
Contrary to his public CV, the New York Times reported that Citigroup and Goldman Sachs have no record of Mr Santos ever working there and Baruch College could not find a record of Mr Santos graduating form the university.
Friends of Pets United, the animal rescue group Mr Santos claimed to have started, is not a registered charity with the US's Internal Revenue Service.
Several of his fellow Republican politicians have called for Mr Santos to resign from his New York seat, which he won in the November mid-terms.