That's what some Chicken Littles say, who are always saying that the sky is falling in one way or another. The dumbing down of the US won't be complete unless Chump is actually elected President. He hasn't been nominated yet, and if he is, how many Republicans will stay at home or actually vote for Hillary or Bernie on Nov 1? Greater than the number of Democrats who would stay at home or vote for Trump if their favorite isn't nominated, that much is certain at the very least.
What we're seeing here is the break-up of the Republican Party. Clearly, Trump is firmly in control of the dumbest and loudest part of the party, but it's not the whole party. The whole Republican party hasn't elected a President since 2004. One part of it hasn't got much chance.
Other than staying at home or voting Democratic in November, there could be a 3rd-party run by a Republican, which would amount to giving votes to Hillary or Bernie without the 3rd-party candidate admitting that that's what he or she is doing.
And I repeat: Chump hasn't been nominated yet. If he goes into the convention without a majority of the delegates, and it turns out the the number of delegates who hate him actually is greater then the number who love him -- which wouldn't surprise me a bit -- and Rubio or Cruz or Kasich or somebody else gets the nomination, what are the chances that Chump won't run 3rd-party? slim to none, I think. And Chump as a 3rd-party candidate with Rubio or Cruz or Kasich or somebody else as the GOP is even better for the Democrats than the other way around, I think.
So, instead of screaming that the sky is falling, just keep screaming about what a loathesome bigoted idiot Chump is, and trust that the louder you scream the more people will hear you.