What would your reaction be to a president who intended to hand over US sovereignty to a foreign power

I guess that would depend on which foreign power. It could be an improvement.

and merge your country into a federation with a different flag, a different currency, and a mishmash of different, and conflicting cultures

With the exception of the flag and the currency, this is what we have now. A mishmash of different and often conflicting cultures. Many of us are pretty used to it by now.