I doubt there'll be a holocaust (no one will be willing to take the blame), but the US will definitely enter a period of decline as no one will be looking to correct its inertia nor stand up for its values beyond vague 'stern statements'.
It'll be a Biden Regency, worse than the Bush presidency. Assuming a Harris VP (who doesn't pose a threat to the Obama clique), it'll be run by the cabinet, bureaucracy, consultants, and think-tanks, all of which have no particular interests in fixing the country's problems, and who instead seek to profit off its inefficiencies and problems (i.e. Obamacare, student loans, procurement, legislative pork-barreling). There is a reason why the DC suburbs are among the wealthiest in the nation, yet seem to produce little of value.
Meanwhile, domestic and foreign policy will return to apologetic butt-kissing while Russia and China run rough-shod over strategic areas, much like they did during the Obama presidency. The economy policy will be more consumerism, while the US increasingly produces little of strategic value as globalism returns as the policy of the day.
Would feel very much like the Late Roman empire as the systems ossify because the powers-to-be have no intentions of changing course and damaging their vested interests. There is no American imperial transition as some might dream, because the US is already an empire in all but name IMO.
At least the US would regain its 'diginity and presidentialness' as it begins to slip beneath the waves, right?