Donald Annoying Orange is an IRL troll. His whole campaign is just him making moronic controversial statements to get smug idiots to do his advertising for him. The more you spread this bait around the more likely he will actually win the election.
That's not really an issue here. It's a minority of users who are both US citizens and capable of voting here.
Compare their Twitter followers as well: Annoying Orange has 6.16 million and Sanders only has 1.43.
This isn't surprising at all. Bernie Sanders is a career politicians, so he's not likely to have a significant amount of Twitter followers, and I'm sure only has a million because he is now campaigning for presidency.
Annoying Orange however has been in the public spotlight for years, including having his own TV show. So he is going to attract more Twitter followers, being a somewhat more traditional celebrity seperate from his recent politicking.