You are operating under the assumption that Trump's attack on Iran are for the benefit of Americans. Maybe that isn't the case.

I don't make that assumption. I think Trump is motivated primarily by: i) wanting to be as consequential a President as possible; and ii) never being thought to have lost in something.

I think he has a simplistic belief that all that's necessary to "fix" some of these longstanding problems is just killing (or threatening to kill) the leaders of the country. He has a Great Man view of how the world and history works - change the leader, and you've solved the problem. He doesn't think these festering issues of global geopolitics linger because they're due to macro factors or historical forces that can't be solved by shooting. The persist only because past Presidents were too weak to do anything.

And in Iran, he can't bear to have been told "no." He told them the nuke program had to go. He demanded. He insisted! I'm sure he threatened that if they didn't follow his orders, they would pay the price - and still, they refused. He was balked, and he WILL NOT BE BALKED! So the only thing for it was to attack. Not because he thought the attack would get any particular future outcome other than demolishing the people who said no to him; that was the goal. Punish the people who said no. So that's why he thinks this is a war that's already been won. For him, it has!