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.