One term Presidents since 1950 - it's varied. Marginal communication skills, war, economic disaster, age, chaos, scandal, third party candidates
LBJ - Mishandling of Vietnam, inflation, assassinations of MLK, RFK, Chicago riots, American cities burning. It was a real mess.
Ford - solid POTUS, but very dry, marginal communicator, pardoned Nixon/Watergate fatigue
Carter - high inflation + unemployment (misery index), Iranian hostages, second oil/gas crisis
41 - solid POTUS, marginal communicator, whacky 3rd party candidate in Perot, looked at his watch
Trump - agent of chaos lies, bogus personna created on TV, COVID, stupid daily tweets, weird cult
Unfortunately, Trump LIES and Disinformation re: FEMA and hurricane have made this election a virtual tie. There's an abnormal morpheus effect of the Trump Firehose of Lies. Just a couple would sink any campaign, but the firehose and MSM sanewashing provides Traction.
Harris is a solid communicator. If she were elite like Obama, Clinton, or Reagan, she'd win handily.
Let's assume Trump loses - does he slink away or hopefully fly away to avoid extradition? Does MAGA allow the GOP to return to normal. Can it return to normal?
Would a Nikki Haley be able to challenge? I think it would be difficult. She's been Governor, but South Carolina as state has major economic disparity and incredibly poor areas where people like in shacks and old school buses. DeStantis has the personality of sandpaper. Abbott is delusional and power hungry. It's a reasonable assumption of Kamala wins this year and the economy remains status quo, she would prevail in 2028.