It's called the first amendment. If people are not allowed to make satire about a billionaire who may become president, then where did the first amendment go? Look, nobody is free from satire, and nobody should be. If someone hurt your feelings because they said some mean stuff about you on TV, suck it up. It's not the end of the world.
Yes, actors should be permitted to make impressions of Donald Trump. No individual should be exempt from caricature, and by extension criticism--least of all one with aggressively controversial political stances and candidacy for the United States presidential election. People working in the media, including actors, should be able to reach out to the public with satire and alternative narratives. People in countries where the media has been restricted from commenting on public personas live under a great deal of oppression and this isn't what the United States stands for.
Actors should be allowed to do impressions of Donald Trump. Last time I looked we have free speech. And parity is a form of free speech. Similarly, actors should be free to do impressions of Bernie Sanders or Hillary Clinton. Of course, we see far less of it because actors are overwhelmingly left leaning, so they find it less fruitful to mimic one of their own.
Comedy doesn't just make us laugh, it also makes us think. When actors do impressions of, or impersonate, the Presidential candidate Donald Trump, it allows us to consider more deeply the implications that his presidency would have on our democracy. I therefore believe that actors should continue to impersonate him as they please.
Yes, Donald Trump doesn't deserve any special treatment; all politicians have been impersonated in some manner in a satire sense, namely on the show Saturday Night Live. Shows like this and the Colbert Report have actually done a great deal to discredit the agenda of politicians like Sarah Palin and Mitt Romney, all while entertaining the world. It is an established occurrence in American culture and Donald Trump should not be shielded from it.