I like to thin foreign influence campaigns had a lot do with it. Everything these people are doing is like a playbook of destruction seen all over the world during the cold war and beyond. The heritage foundation and GOP leadership have heavy russian influence. Social media influence campaigns don't help either.
Something a lot of people aren't considering is that a dictator ship might become a reality and these people will succeed, the US will decline but still remain a powerful country but with constant internal strife and divisions. The real goal seems to be curbing American influence overseas, and containing the US, just like the US tried to contain Russia and China for decades prior.
The US military/intel community literally used sitcoms to influence the middle east in the 2000's. What goes around...
The other half of it is the GOP long ago put themselves up for sale to the highest bidders. Those high bidders used to be the American business community, so they'd work to pass legislation that helped existing US businesses at the expense of US citizens [0]. But at least the US as a whole remained the world leader. However those high bidders have now become foreign interests, so the policies are directly aimed at hurting our country.
I think this is the real outcome of having so much debt owed to foreign countries. The political kayfabe all focuses on it like it's some mortgage where other countries will foreclose or whatever. But there is no mechanism for that to actually occur. What it does allow those foreign countries to do is to buy up significant chunks of the US, and then exert the control that customarily comes along with ownership.
[0] this is also why they'd constantly rage-farm about immigration, but then turn around and facilitate the supply of cheap illegal labor