US do have a debt problem, but at this point as long as US is able to maintain its military, it should not worry.
The way I see it US enjoy its current advantage mainly from 4 aspects. 1. Economy. 2.PR 3. Soft power 4. military.
1. Economy has suffered the most, since US let the bankers play casino with US housing/banking industry, it almost plummeted into a world wide depression. The legitimacy is of US economy's supremacy is gone. China is also challenging silicon valley, and trying to build up the new economic network right now with their trade lines. so I don't see US will maintain this monopoly for long, this will be the 1st pillar to crack.
2. Propaganda, US has always controlled the narrative of western world's opinion, and now look like Russia and the internet is doing a good job challenge it, and I see them losing more control. This will crack second.
3. Soft power, still holding up pretty good, Hollywood is still pretty dominate, US culture is still widely admired. For all that China is done, their soft power still sucks overseas.
4. Military, you can argue that US military's sense of invincibility has been very much shattered by Afghanistan/Iraq, however they fact that they still have 400+ bases all around the world, and the nations that let them host those bases, says much more.
And the most important thing of all, as long as they protect the Saudi and GCC, the Saudi will sell oil in USD. For better for worse, US is still the guarantor for security for most nations in the world. For this, China is no match, because they are trying to outplay US in the economic game, which is a smart move.
As long as US can maintain this vast military network, the they will be able to exchange printed piece of paper for goods and services. For that, maybe Donald knows something.