LBJ got 48% of the vote in the 1968 New Hampshire Democratic Primary

[Tom Rinaldo]

That was enough of the vote for him to win it, but not enough of the vote for him to stay in the race, and he subsequently withdrew. Let's see how well Trump does in New Hampshire. Trump only got 51% of the vote in Iowa. Yes LBJ was the incumbent President in 1968, and therefore the degree of support he got from his party in NH was deemed disturbingly low. Trump is not the incumbent, but he is the most recent Republican ex-President and roughly two thirds of Republicans think Biden illegally deposed him, and that Trump should rightfully be President today. The fact that Trump may do no better in New Hampshire than LBJ did when he was "forced" to abandon his bid for President is unlikely to be viewed through that lens, but it hardly indicates that Trump will enter the 2024 campaign in a strong position.

[TwilightZone]

1. "it hardly indicates that Trump will enter the 2024 campaign in a strong position"

The fact that he's up 50% nationally is a better indicator. His lead is currently the largest it's ever been.

This isn't 1968, and there are no precedents for the current situation with Trump.

"Trump is not the incumbent"

He essentially is, though. He never stopped being the GOP incumbent in every way that matters.

[Tom Rinaldo]

2. Trump essesntially is the incumbant President to the vast manority of Republicans

That's the point. Given that, Trump's level of support inside of the Republican Party is much less impressive than it might otherwise seem. Would 49% of Democratic caucus goers have voted for someone other than Joe Biden had there been a Democratic caucus in Iowa? Seems pretty unlikely. How much support did Obama have inside of the Democratic Party in 2012, or Bill Clinton among Democrats in 1996, or George W. Bush among Republicans in 2004?

Trump is on course to lose more support among members of his own party, when viewed through the lens of quasi incumbency, in a Presidential election since at least 1980, when Reagan beat Carter in a landslide.