The US has become much weaker compared to 20 years ago

It has become much weaker as we transitioned from a unipolar world to a multipolar one following the collapse of the Soviet Union.
To be precise, it's not that the US itself has weakened, but rather that its allies have become too weak.
The US share of global GDP has dropped from 30% to 25%,
but if you look at the share of global GDP held by US allies, it has plummeted from 65% to 45%.
Naturally, that demand was swallowed up by China—the opposing force to the US—or
by the Third World, which claims to be neutral.
Even if we set China aside, these countries are not friendly toward the West and act independently.
Given their nationalistic sentiments,
there is no way they would simply follow orders.
As for military power, while it has grown by absolute standards, it has weakened relatively.
From the industrial base to cultural factors, everything is currently not conducive to war.
Just 30 years ago, they could control Europe and Asia simultaneously, but they have long since hit their limit, well over 10 years ago.
It's not that the US is no longer a great power, but it has been quite some time since they stepped down from being a superpower,
and adding a madman to the mix just makes it worse. smh