The Middle of the Road
Go back with me to the 1992 election. In September, just 2 months before the election, Bill and Hilary Clinton were named as witnesses to the insolvency of Madison Guarantee Savings and Loan, specifying related problems associated with Whitewater Development Corporation. Conservatives jumped on this as a way of discrediting Clinton, despite the FBI turning down the investigation saying it lacked merit.
For 8 years conservatives hammered Bill Clinton on Whitewater, a succession of supposed mistresses, lying under oath about the relationships and everything they could find. The harder they tried to paint him as an immoral womanizer, the larger his support. He received 43% of the vote in '92 (third party candidate Ross Perot received 19%). In 1996 he received 49% as Perot dribbled down to 8%.
In the 1990's Republicans were able to pick up House and Senate seats and held control in Congress, but despite all the rhetoric, they were unable to unseat Clinton.
In watching the events surrounding the 2016 election, I am struck by the similarities. Liberals were outraged by nearly everything Trump said before the election. But the outrage before the election doesn't compare with the outrage after.
What neither the Republicans of the 1990's or the Democrats of now understand is that elections are never decided by the opinions of either extreme. They are decided by those who are in the middle, who don't have strong opinions and who make up their minds as a result of a strange mixture of issues and who makes them comfortable/uncomfortable.
Clearly, Republican bashing of Clinton was counter-productive. What liberals don't see is that bashing Trump for everything is just as unproductive. As a devout middle-of-the-roader, I voted for neither major candidate. In talking to friends, my liberal friends are frothing at the mouth over how awful Trump is. Conservative friends just kind of smirk and say, "It's going to be fun." But in between, the moderates I see are looking increasingly uncomfortable by the attempts of the liberals to force them to either side with "reason" or admit they are racist, misogynistic, ignorant savages. After 4 years of this kind of treatment, they will end up voting for Trump, just as they did for Clinton in 1996. And yes, many of them will be the same people.
What committed extremists don't realize is that "You either agree with everything I say or you are an idiot" is NOT persuasive. If a moderate Democrat were nominated in 2020, I would be inclined to vote that way, but I strongly suspect I would be in a tiny minority of moderates. This is shaping up as a huge win for Trump in 2020 already.