Both Bushes ran into the ‘bad experience’ problem for their second term, Bush Sr.s economy and generally unpopular presidency meant that his time as President didn’t help him against Clinton. The Democrats were dumb enough to run another Senator who supported the Iraq war as their anti-Iraq-War candidate, so they weren’t really able to use W Bush’s record against him like they could have with an actual anti-Iraq-War candidate.
W Bush pre-presidency was governor of Texas and got several major initiatives that he backed through the legislature (tort reform and school choice are the ones I remember), both of which were positives for his voter base even if most people on this board (including me) don’t like them. He didn’t have anything that he was backing away from on his record, unlike Hillary Clinton with the super predators and Iraq War.
That’s what I can think of off the top of my head. I’m not really up for in-depth research for a message board post, especially things like Nixon’s pre-election history that happened before I was even born and probably aren’t readily accessible on the internet since they happened before routine online archiving.
Oh, meant to add: McCain had the experience advantage on Obama, but neither of them had serious executive experience, and McCain also IIRC lacked any spectacular accomplishments. For his second Term, Obama had a very successful first term as president to fall back on, that list of accomplishments is pretty big.