Well, why not believe it? Who would believe a president of the U.S. would still be lying about getting defeated seven months after an election? Or try to force his veep to suborn the constitution? Or actually get on a phone and try to get an official of a state government "find" votes for him? Or incite a riot at the Capitol Building?
Trump did all those things. Because he's a narcissistic man-child who can't accept defeat. Why not believe he really thinks he could still get reinstalled in the WH after all his previous lunatic behavior?
Carter never did that. The Rodents came up with some looney-toon crackpot theory that GHW Bush flew to Paris in an SR-71 Blackbird to meet with some Iranian trash to talk them into hanging on to the hostages Carter didn't care about until after Reagan was elected. Then Bush flew back in time for breakfast so the gaggle of media surrounding him didn't notice.
That must be what you're discussing since there's no other recent president who lost a second term bid, except GHW Bush, in small part because of the above mentioned nonsense the Rodents emitted. But Rodents emit that kind of nonsense as frequently and as reliably as a bison in Yellowstone.
Other than that, all presidents since GHW Bush have won re-election. Name one that hasn't won the election.
In fact, there was even a guy, a famous TV personality and builder who was the best president in decades, who garnered an unprecedented 75,000,000 votes, minimum, more than any other candidate in US history.
His re-election was stolen, of course. Nobody believes that 81 million living breathing people could casts their one and only ballot towards a senile Marxist pedophile.
You don't believe that, do you?