It began with the National Review. The National Review influenced Barry Goldwater, who captured the Republican nomination in 1964, ending the rule that only a moderate could be nominated for President by a major party. The culture wars of the 1960s and early 1970s divided America, as did the Reagan Revolution. It really went off the deep end when Newt Gingrich established a doctrine for congressional Republicans when a Democrat is in the White House: make wild accusations, never compromise, always obstruct, have hearings on everything, etc.
So it is just the Republicans fault? Democrats don't have any part in it whatsoever? Ok.