Actually liberals have been issuing this warning for a lot longer than that. One might even say forever. But this specific spasm of outrageous extremism really hit its stride in 1998 when it impeached a duly elected president over a personal indiscretion and turned politics into an embarrassing tabloid obsession. This may seem like a trivial thing now but it was their first serious foray into the breaking of norms and rules of governance that had up to that point kept the system running with at least baseline efficiency. When they pulled out their partisan IEDs in the 2000 election they proved all bets were off.
This form of slash and burn politics has always been part of American politics on some level but this latest iteration hit warp speed in the 1980s when Gingrich and the back benchers, followed by right wing media, started making their move. Trump is the inevitable result.
Not to blow my own horn, but I’ve been saying it since way before Bill Clinton became president. I saw it long before Ronald Reagan perfected the dog whistles about welfare queens and the GOP getting in bed with the Moral Majority in the 1980’s. I am old enough to remember the scare that Barry Goldwater put in me at the tender age of 12 with his talk about “extremism is no vice.” In my lifetime we’ve had Joe McCarthy and George Wallace, and when the former governor of Alabama decided to run for president as an independent and I saw the crowds he riled up, I saw the dark side of the white people who were more afraid of the idea of a black child in their white school than they were of being able to earn a wage to feed that child.
Donald Trump is not just the inevitable result of a quarter-century of extremism; he’s the newest model.