Stock market is up ~10% since November, what's the deal?

Certainty. Before an election there is uncertainty and consequently an unknown risk. Elections remove the uncertainty irrespective of who wins what and make the risks more knowable. The business cycle reflects the elections. Rising stock markets are one form of business cycle expression when alternative investments are less attractive: e.g. if the money markets were returning 6% stock prices would probably be lower.

It is probably speculation. There is a certain kind of rich person who likes to spend their money to make the Republicans look good. Often, for instance, prediction markets lean Republican because there are deep pocketed "investors" who don't mind losing money for their cause.