Trump was not a lifelong Democrat, he's been a Republican longer than anything else but he's hopped around from party to party over the years. The only time he was ever registered Democrat was during the Bush years and Dems were a hell of a lot more moderate back then. Nevermind he's got a pretty proven record in office now. Certainly not perfect, but the bar is low enough he's been leaps and bounds better than any President in the last 100 years. RFK Jr and Tulsi throwing their support behind him in the election doesn't really have broader implications for the party, this election is just that fucked up but it's not like RFK Jr is suddenly the face of the party.
The GOP in general has been moving away from the far right evangelical pandering back towards it's more libertarian roots. Still has a long way to go, but the RINOs are slowly dying off and there's plenty of younger people within the party that look promising.
The Mises caucus has essentially taken back over the party and thrown their support behind Trump unofficially this year because they felt another 4 years of Biden was such a threat. There's been a huge shake up in that party since all the bullshit in 2016 and 2020 but their candidate this year is not meant to be a serious candidate. He was intentionally picked to force libertarians to vote for Trump.
In general I don't support the Libertarian Party despite leaning heavily towards libertarian ideals. I'd much rather see them join the GOP and steer that party back towards championing individual liberty and fiscal conservatism. Especially now that they've kicked out the fake leadership and taken back over the party. The last thing I want to see happen is they run a solid candidate in 2028 that has no chance of winning but siphons off enough GOP votes to let the Dems back in. It's going to take more than 4 years of Trump to undo the last 4 years of Biden.