If he chooses to run for a second term - and as far as I know there's no law saying he has to - I am 98% sure he will win.
Yes, I'm sure he has already been a disappointment to many of his supporters, and will continue to be, but they're not going to switch their vote to the Democrats if they think it just means change for the sake of change. They will only switch their vote if they think they're getting something better. And if he delivers on infrastructure, trade agreements and jobs then he may be able to persuade people to vote for him who weren't persuaded the first time around.