…[P]robably the greatest example of party durability is seen by the Democrats, who, in 1866, found themselves on the wrong side of the Civil War. That is, as we dryly noted when I practiced law, a bad fact. The party didn’t even field a nominee in 1872, instead endorsing the Liberal Republican candidate Horace Greeley (who died before the Electoral College voted). Yet in 1874, the party picked up an astonishing 94 seats (which would be 140 seats under today’s terms). Two years after that, Democrats won a majority of the popular vote (yet lost the Electoral College in a disputed election). They won the presidency outright in 1884, less than a decade after the end of Reconstruction.
So even assuming Trump loses badly (I think he will, but it is too early to say anything definitively), it is nevertheless unlikely that he destroys the GOP. The American public has historically had a decidedly short-term focus on elections. If the Republicans can come back rather quickly from overseeing the Great Depression, and if Democrats can come back rather quickly from losing the Civil War, we should expect any damage caused by Trump to be fleeting.
Source: The Real Reason Trump Can’t Break the GOP | RealClearPolitics