Trump... faaaaaar from perfect. But the reason he's made it as far as he has? Because people are sick of career politicians (Jeb, Marco, Cruz, etc) who make promises then proceed to fuck the voters.
Hillary is the worst of the worst examples of Corrupt Rich White Bought-And-Paid-For Politicians.
Because the Republican nominating system's non-proportional allocation of delegates, combined with the schedule of Republican primaries and caucuses, is designed to very strongly favor the candidate with an advantage in early name recognition especially if they can effectively appeal to a particular demographic that the Republicans have been focusing on as a key element of their coalition since Nixon's southern strategy, especially in a crowded field since the system is designed to create artificial delegate majorities from small electoral pluralities.
(This is engineered as a way to shorten the competitive period of primary contests by making a candidate's victory nearly inevitable very early in the process without them needing to secure anything like majority support even within the primary electorate, allowing the party to move quickly on to focus on the general election.)
Trump and Bern should, by all reasonable definitions, be on "other" platforms. Trump is, if anything, independent... Bern is much further left than the normal "Democrat"... But anything outside of these two "buckets" has no chance.
90% of people don't fall fully into either of these buckets. These buckets drive "us vs them" partisanship that's only gotten worse and worse in recent years. Don't agree with the GOP 100%? RHINO (Commie! Socialist! etc)! Don't follow DNC? DINO (and Racist/Bigot/Islamaphobe/etc)
I'm not sure how exactly I would change it... but there needs to be more than two parties.
I sure as shit know I don't fall fully into either camp although I'm definitely more right than left.
1) not a supporter - people who sue widows are pretty much on my not nice list