Yeah we're one-terming it at this point if people don't get complacent
Don't be so sure. An incumbent President is always a much stronger candidate. If Trump sticks to what he promised his, largely white, voters, he will maintain that vote in 2020 but will have the full funding of the GOP behind him.
Think about everything everyone said before the election. Trump had the highest disapproval of any candidate and won and won big in the electoral college. Granted he will lose some of the hispanic vote, definitely the black vote. It is still crazy to me that American white women had the chance to elect a white woman as President. The first female President and they chose Donald J. Trump.
But people are predicting that ISIS will be defeated on his watch, the economy which was improving under Obama's watch will keep improving under his and he will get the credit. The democratic party would need to have a lightning in a bottle candidate like Obama, charismatic and more mainstream overall appeal, to show why Trump shouldn't be re-elected. 4 years is still a long ways away. This left tea parry movement is strong though. Build some momentum and we'll see a strong pushback at all levels of government.