Ask Lemmygrad

Indi has a couple articles on the subject from a couple years ago:

https://indi.ca/nothing-to-see-here-just-the-wheels-falling-off-empire/

https://indi.ca/how-americas-military-has-fallen-apart/

The US military can still do damage even in its state of decline, but as Iran is showing, its two main strengths are air defense and aerial bombing (air superiority more generally), and if you have enough missiles to overwhelm its air defenses and destroy its early warning systems, and you have enough air defenses to stop it from wreaking havoc just anywhere, the cracks start showing fast. Its navy is clearly struggling and in the context of Iran, ground forces would struggle to gain any traction due to the terrain.