Even if there is a slowdown or recession which spills into 2020, Trump can do various things to trigger short term stimulation of the economy, including trade agreements he is in the process of leveraging with hard line positions, or ordering the Federal Reserve Chairman to cut interest rates. It will all depend on the pre-election polls and the timing. Long term, the economy is cyclical regardless of who is in office, but whomever is in office can make moves that trigger short term stimulus. For these reasons voters should always be careful about allowing manipulations of the economy that result in short term trends to influence how they vote. You have to be in it for the long haul or not at all.