For now post Pax America is merely a fantasy that reveals a lot about the people that think it's happening now (they're showing their personal preference). The same things were said due to Trump's first term also. Instead the US got more powerful and far richer in the time since then.
Back in reality, the 1860s, 1930s and 1970s were worse for the US than anything going on now. The 1930s were drastically worse. The US as superpower has survived far worse than Trump and it'll do it again.