Former Trump Justice Department head William Barr, in the course of reiterating his strong preference that his party nominate a less deranged presidential candidate next time, expressed a fear that has been in wide circulation: If defeated in the primary, Donald Trump “will burn the whole house down by leading ‘his people’ out of the GOP.” One version of this is that Trump will either form a third party or simply refuse to endorse another Republican, thereby dooming his party’s chances. Those of us considering the question from a less friendly standpoint than Barr — I consider the Republican Party...