This is a pretty empty threat. Realistically speaking the US cannot escalate without facing huge domestic backlash. Public support for US involvement in a new war in a is nonexistent, given the abject an expensive failures of the recent afghan and iraqi wars.
Add the fact that any iranian involvement would go through hezbollah, gives both the us government and iran a way to plausibly deny iranian involvement. The US will do nothing. They might send some troop to “support” israel. They already have. Which is a token gesture at best.
I read somewhere that a group of 55 republicans who plan to make sure he gets less votes every round. To rub in how much they don’t want him.