They’re both running to try and lose the election.
Trump never wanted to win in 2016 in the first place, now he just wants to raise money to pay lawyers to beat his court cases, not become president.
Biden said he would only serve one term as president, because he was old. He doesn’t want to be president again, which is why he is trying to become a unpopular as possible.
Trump does have shades of Caesar, in that he's mostly seeking office for the immunity it offers rather than to exercise its powers. Part of him also has an ego about the amount that being POTUS lets him be on TV.
Not OP but I've read Parenti's book on this topic and I would recommend it. He uses the case of Caesar to make a good point that a lot of historians don't like and a lot of people who skim the material misunderstand.
The thing that Trump would like more than anything else would be to become king in a constitutional monarchy. It would stroke his ego, people would have to respect him, the law would be unable to touch him a d he wouldn't have to do any actual government business.
when did Biden say he'd only serve one term? I doubt he's having much fun, but he's had plenty of opportunities to appoint his successor. even if he'd rather not be president, his ego is so massive that he thinks he's the only one who can handle the job.
He never pledged to run for one term, he made several statements that he was a bridge to the next generation of leadership he did not expect to run for a second term but he never explicitly ruled it out.
I would post a link but I'm not a lib, you know how to Google, and the best article looks like it's from the Atlantic which I refuse to give free clicks to.
But TLDR, yes he made very clear he planned to run for exactly one term. No, he did not promise or pledge to run for one term.