I thought at first that he was likely being blackmailed by Israel - it's near certain that the Israeli government has at least as much evidence of his serial child rape as the US government does.
Mostly based on the way the whole war played out though, I tend more toward a different theory now.
I think Bibi convinced him that overthrowing Iran would be a cake walk - that just like Venezuela, they could go in fast and bomb the shit out of things and get rid of the Ayatollah and take over, and then Trump could get Narges Mohammadi out of prison and she'd be so thankful that she'd give him her Nobel medal, and then he'd be the bestest President ever in the history of ever because he'd have two Nobels (well - technically, he'd only have two Nobel medals, and claiming that he has a Nobel because he has a medal is sort of like claiming he's a Super Bowl champion because he has a ring, but he's too stupid to realize that).
And everything played out just as intended, right up to the point that Iran didn't collapse and instead just calmly set about replacing the Ayatollah and systematically bombing American bases and property all around the Middle East while closing down the Strait of Hormuz. And he's been desperately flailing around and throwing tantrums ever since, because that wasn't what Bibi promised.