Elon Musk is one of the world’s richest man and has a lot of power behind all that wealth. It's no secret that the man is actively supporting Donald Trump in the U.S. presidential election. Yes he's a US citizen and so he'll have to support someone at least but powerful men like that don't support politicians just because they have to select one as their responsibilities as citizens, there are reasons behind it, always.
Elon Musk has already donated a lot of money through his political action committee, America PAC and is also publicly endorsing Donald Trump.
Most business men and leaders try their best to stay out of the spotlight when it comes to politics because it can affect their business directly. Imagine someone who's a Tesla fan hates Donald Trump and just because Elon supports him, they stop being Tesla fans, that's going to be a problem and that's why it's unusual that Elon is open with his stands.
He has already given out $1 million to random voters just to encourage people to register and vote. A lot of people say that Elon supporting Donald Trump is connected to the fact that he hates the government regulations of the Democrats.
He believes all those many rules have slowed down the progress of his companies, Tesla and SpaceX to be precise. He's hoping that maybe if Trump wins, he can help reduce these regulations so it's a matter of personal interest.