It would be a total disaster for the US.

A Republican Administration would be authoritarian, verging on totalitarian, and a gutting of the most important Federal help implemented by FDR. It would mean (if it hasn't happened already as some argue) a takeover of the government by corporations which is a classic definition of fascism. It would mean continued monitoring and harassment of anyone critical of the Administration's policies (as seen exemplified by the Bush years) and the rise of the misuse of police force to enforce this monitoring and abolish peaceful protest.

The use of weaponry on the streets would not be curbed but encouraged by a misreading
of the Second Amendment and lobbyists for the NRA.

"Trickle-down" economics would result in deflation and division of economic classes of people (have-and-have-nots). Important government programs would be cut.

The US has already lost its industrial base because of the activities of the GOP and Wall Street. This would continue and the US would have (as it does now) its chief export,
arms and weapons.

Social services would be impotent. (Some argue that they already are).

If Dems get in, there might be a chance that some of the more level-headed minority ideas in Congress and the Senate could prevail even if that looks bleak.

If the GOP gets in, forget unions, minimum wage, social safety net, job growth, and expect more sabre-rattling.