Someone in Reddit succinctly summarized why Vance was picked for VP and why he's now a liability.
https://old.reddit.com/r/changemyview/comments/1fj4ynw/cmv_jd_vance_being_the_chosen_vp_was_one_of_the/lnly3hi/
Ok here we go, I am going to defend the Rs and JD Vance (well kinda TLDR at the end).
JD Vance was an incredible brilliant pick at the time. JD Vance (Im talking about the 2020-2024 JD Vance here not the old one) had a couple of pro's and a couple of cons.
PROs
1) Trump desperately and I mean desperately needed money in May of 2024. Look at the cash on hand metrics here https://ballotpedia.org/Presidential_election_campaign_finance,_2024. JD Vance was able to give him a large influx of cash from his very very close connections to Peter Thiel (Billionare former CEO of Paypal and huge in the silicon valley world). This connection also allowed Trump to form a bond with one Elon Musk, which allowed him back into the non exclusively right wing social network sphere, get a bunch of desperately needed funds, and have a very vocal and influential member of society in his corner. I want to make clear here, there were a bunch of reports that the money that came in June was from silicon valley and the tech sector, signaling the pick, but admiditly the bump from Jun-July is smaller. JD Vance did bring in a bunch of money but he may not have been the only thing causing that bump.
2) Trump liked JD Vance, because JD Vance is an ass kisser. JD Vance became a valued member of MAGA especially in the leadup to the 2022 election, where he doubled down on the MAGA base in Ohio and won an election to the senate (more on this later). Alignment and fealty to Trump are super important.
3) JD Vance is an attack dog in the media. He is very good at barbed language and speaking in an authoritative way. He is also not the worst spin doctor. You have to remember, the R's were running against Joe Biden. Joe Biden was a weak candidate, and there is a base part of the human psyche that prefers our leaders to be strong. Thats what Trump gives to a lot of people, the appearance of strength. The Republicans thought if they nominate an attack dog to make Biden look weak, they could cruise to an election win with Trump having the advantage at the time anyway.
4) JD Vance is heavily, heavily involved in project 2025. He wrote the forward for Kevin Roberts' (Project 2025 Architect) new book The Heritage foundation was instrumental in getting Vance on the ticket, with the articles I have read mentioning that if Trump were to go down for 1 reason or another, Heritage wanted one of "their guys" to step into the presidential slot. The heritage foundation donors are also huge donors to the GOP so, more money and keeping their side happy.
CONs
1) People dont really like him. The untold part about the 2022 senate election was that the race was far far closer than it should have been (see I did come back). I want to give some credit to Tim Ryan for that, but it really really shouldn't have been that close, from what I understand due to some really poor debate performances and people in general not getting great vibes off him (people of Ohio please correct me if I am wrong as to why the underperformance). One of the old political adages is that VP picks don't really matter unless they are uniquely bad, so people not liking him was probably seen as something that doesn't really matter to the race.
2) He has always said stupid out of touch things, due to the groups that he has associated with through the years. Lets go back to the Peter Theil and Elon Musk thing. The reason they are in his corner is thats his group of people, thats his circle. See all the weird shit Elon says? That's the people he has been surrounded with since 2017. Against Biden, not a huge deal, as he would have silicon valley behind him, and they were already ahead. Plus making up lies? Who cares if your opponent is to old to respond to them.
So that being said, JD Vance was a brilliant pick for about 6 days, until July 21st 2024, when Joe Biden dropped out of the race.
Kamala being picked immediately neutralized Pro 3, as the "attack dog" mantra doesn't work against a "strong" appearing candidate former DA Kamala Harris. Pro 1 Was neutralized when the race turned and all of a sudden Peter Theil doesn't want to risk it anymore, especially with the Democrats recent crackdown on monopolistic practices in then tech sector. And now that 1 and 3 are gone, Donald has also turned on him because he isn't useful anymore. As for pro 4, the public has woken up to Project 2025 and its disastrous consequences, and is holding it as a major con around his neck.
So now were only left with the 2 cons, 1 pro turned con, and a shit VP candidate.
TLDR: He was a great pick at the time, but the Biden drop out ruined him as a candidate and now they are stuck with him. Lol
Doing edits down here:
Edit 1: Clarified that the money may not have all came from JD
Edit 2: Added carification around why Con1 isnt a huge deal
Edit 3: Thanks /u/CoffeeIs4Closers, added Project 2025 to this explanation