Dropping bombs didn't fail in Vietnam. It succeeded. North Vietnam was defeated militarily. They only took over South Vietnam after the US Congress snatched defeat from the jaws of victory by withdrawing funding so the US troops had to leave.
> The claim that the US will beat any country isn't backed by any evidence. At all.
Certainly it is. Given a clear objective, the US military has achieved it in every case. The reasons that the US often fails to capitalize on such victories are political, not military.
> the Gulf War? Which just ended up leaving Saddam in power
Because removing Saddam from power was explicitly not a military objective in that war; the military objective was to drive Iraqi forces out of Kuwait, and that objective was met.
When the US decided it did want to remove Saddam from power, in the second Gulf War, it succeeded. Again, the reasons why the aftermath of that war became a debacle were political, not military.