Hi i'm a poli sci anon and worked in a state legislature for a little, lemme give an informative polisci analysis of why Vance. Trump picked Vance because, at the time, Biden was still the democratic pick for president. Polls showcased that Trump was way more likely to win the election, so they felt confident taking Vance despite him being a risk. Vance, although he denies it, is tied into something called Project 2025 (wrote part of it too) that is basically a policy and structural framework for Republicans once Trump gets the presidency again. Project 2025, if enacted, will essentially take back things to the 1950s and strip POC and Women of their rights. It's genuinely scary. Trump picked Vance despite a lot of Republicans not liking him (Vance has a history of talking shit about poor people, not being charismatic, and being inexperienced) because he would further the 2025 agenda and maybe, over the course of a few years, could become more likable and take the reins of Trump cultism since Trump is getting older and won't live forever. Their plan got messed up when Biden did the almost unthinkable thing and stepped back from being the Democratic nominee. Harris became the pick and then picked Walz as VP, a charismatic veteran with a history that includes: being in the army, being a school teacher, is white (so he's marketable to even racist Republicans and the bible belt), and his state, Minnesota, likes him. The fact that he is from Minnesota is a big plus too because it's close proximity to swing states - which are states where their electoral college votes usually determine the presidential race (most states, like California, regularly vote one way, so they are expected votes certain parties can rely on getting. A few states 'swing' on who they support more during presidential races, and they are the ones who usually break the tie and determine the winner. This is also why they get way more rallies and efforts from political candidates) means they already know about him and might be more likely to support them. Trump regrets picking Vance because Vance's extremism is fracturing Republican support, he comes off super uncharismatic and weird, and he had sexual relations with a couch. He's the worst thing possible: unlikable and off-putting, which is harming Trump more than helping. The Democrats are doing way better than anyone ever expected (look at the polls too) because Harris brings younger energy than Biden and Walz is genuinely charismatic, has an amazing trackrecord (he's also pro-union, believes in trans rights, was a school teacher, grew up in small towns so he doesn't give off bi-coastal elite energy, etc.) and has been actually making Harris seem more likeable. If you compare Vance to Walz, Vance has genuinely harmed Trump's race and chances at winning, while Walz has genuinely helped Harris on almost every front. If Trump has picked a nominee less extreme and more likable he'd have a better likelihood of winning.