With so many people pricing in strong economic growth the critical issue will be how many of the pro-growth policies President Trump & the Republican Congress will be able to push through. With every year now seemingly an election year (I heard them talking about the 2018 mid-terms on CNN yesterday), the willingness of Congressional representatives to go along with the policies will be closely tied to the President's approval rating.
As this chart from Real Clear Politics shows, President-elect Trump has a growing approval rating over what candidate Trump had. If this trend continues the President may have the "blank check" the stock market is pricing in. If, however, the approval rating reverses, we could be looking at a serious correction in the stock market.