Creators Trey Parker and Matt Stone have been regularly involved in politics, everything from Kim Jong Il lamentation in Team America: World Police to the President Obama's first election episode which aired the day after voting.
In the episode, Donald Trump becomes the Canadian president and he must be stopped. According to the show, they thought his candidacy was a joke, but they let the joke go too far.
So in very South Park fashion, Mr. Garrison invades Canada to sexually assault Trump to death.
To quote the show:
"Did you hear the good news? The Canadian president has been f*cked to death!"