Those gains were most likely based on the anticipation of tax cuts (increasing consumer spending and the supply of investable capital), deregulation (allowing higher profits, most notably by banks), and repatriation (allowing share buy backs).

So far, none of those has happened and it remains to be seen if they will. If they don't, I don't expect a market decline, but just a smaller total cumulative growth since November that has nothing to do with Trump's election or the general agenda I outlined above.

Tax cuts on the rich don't increase consumer spending, since rich people don't spend all their money (proof: they're rich).

Although this is a popular theory, mostly promoted by the people who don't want to pay taxes.

Tax cuts to the rich increase investable capital, as I said. Trump also proposed tax cuts for everyone else, too, which would increase consumer spending.