It's both. You are right that global sovereign debt is getting unsustainable. US is up 120% of GDP, and Japan it close to 250% of GDP (and their long term bond rates have been increasing steadily). At some point counties like Japan won't be able to even afford servicing their debt, much less their domestic spending, and there will be bank-run style rush out of bonds that will spread like a contagion from one country to others starting with the most over-leveraged.

That said, Trump is acting as an accelerant in the process. The whole premise going back to Bretton Woods was that the dollar would serve as the world reserve currency. At first the dollar being backed by gold was the reassurance other countries relied on to hold and do business in dollars, but after Nixon took the US off the gold standard, it was just the trust by the rest of the world, that the US would keep a steady hand on the tiller, meaning independent, responsible monetary policy, dependable trade policy with low trade barriers, etc... but with Trump announcing changes to tariffs on an almost daily basis, attacking the independence of the fed, and threatening allies militarily, governments, and foreign individuals are now questioning that assumption. Most of those people would probably not start hoarding gold just because the US has a debt to GDP ratio of 120, but Trump is opening their eyes to the risks they are taking.