Isolationism would be perfectly feasible for the US. We have a large country with lots of natural resources, and a skilled population. We could make everything we need ourselves. The only thing that might give us pause is oil and energy.
This would, of course, cause somewhat higher prices and a lower standard of living. However, many of our problems are caused by being too rich for our own good, and we might benefit by cutting back a little.
However, this is probably not going to happen.
Not as a democratic Republic of free citizens. The degree of isolation you describe could only be imposed by authoritarian, if not totalitarian, means.
Such an action would cause far more problems than just "somewhat higher prices and a lower standard of living" here. If it was instituted, it would cause a depression, the likes of which would make the one we suffered through, from 1929 through WW II, pale by comparison.
Should we cut off all imports, all of our exports would be stopped.
We no longer make a large variety of things. For us to get these various commodities, we would have to not only hope the American firms would spring up to make ( those, of course, that could be made, grown, and mined here; that is ) and sell them here. That would take a great deal of time and in the case of some minerals/ores, needed for our armaments, impossible, since none of them exist here.
Your second paragraph is right out of MARX. We're "TOO RICH FOR OUR OWN GOOD." ? You're no conservative.