All he has to do is ramp up the rhetoric a bit. Step up his critique of China by saying that we should probably round up all the Chinamen and other Orientals living in the US until trade tensions settle down. Start saying that we need to "figure out some kind of solution to the Muslim problem" or something along those lines. Maybe start referring to Cruz and Rubio as "my spic opponents", and Hillary Clinton as a "dirty old c**t". His poll numbers will be back on track in no time.
The saddest part about this post is that that might legitimately help him.