This is my honest assessment of the calculus of the move. Please don't interpret any of this as me personally supporting or approving of these motives. I'm just trying to have a genuine intellectual discussion about the potential thought processes of our collective leaders.

* Quick, victorious wars can be incredibly popular domestically, regardless of whether surveys say that only 16% of the US population supports the war. Trump needs an approval ratings boost. The global tariff shock was a PR disaster. A quick, victorious war is a tried-and-true approval rating booster over the last 200-300 years. The key, of course, is actually keeping the war truly short and victorious. If it drags on, or if people start asking "have we truly won?", then that's a whole different matter.

* We have moved out of a unipolar geopolitical world and into a multipolar one. The USA is checking the ambitions of the rival powers. Want to invade Ukraine? Sure, go ahead and try, but it will be a multi-year slog. Want to go for years maybe developing nuclear weapons, maybe not, and making US antagonism a central part of your political platform? Watch us systematically attack your nuclear program and and air power and do highly targeted assassinations of your political elites over the course of two weeks. Want to invade Taiwan? Look at what happened in Ukraine and Iran and maybe reset your expectations about how that will pan out.

* There has been a lot of questioning lately around whether the US will actually help their allies when they're in a pinch. This is sending a pretty strong message of reassurance to allies.

* Trump may actually want things to escalate to a point where he can reasonably declare martial law within the US. How do you stay in power when you've already hit your two-term constitutional limit?

Your question was "how does it benefit the US?" but I don't think that's answerable because everyone has a different take on what's best for the US. It's much more feasible to discuss "how does it benefit Trump?" or "how does it maintain US's position as a world power?"