A large part of the problem is the American people allow them to get away with it by not voicing their dissatisfaction verbally and at the ballot box.
Unfortunately, the political parties pretty much control which candidates are offered for the American people's consideration. Without party support, it's pretty hard to get elected and that support is contingent on sticking to the party line. Trump was a rare exception.
I don't know enough American history to say what politics were like prior to the 20th century. (From what little I have heard and read, they were pretty rough.) For most of the 20th century, the Republican and Democratic parties weren't that far apart. More importantly, members of each party usually respected, and often liked, each other. Beginning at the 1968 national convention, the extreme left wing took over the Democratic Party. The extreme right wing did the same to the Republican Party in the early 1980s. They no longer disagree about the best policy for the country; they hate each other's guts. As a result, neither party represents the majority and it shows in the candidates that make it to the ballot.
I didn't vote for Trump last fall because I like him or consider his policies, whatever they really are, to be wise. I ranked the four candidates and he came in fourth from the bottom.
