The neocons are right that a Trump presidency would likely be a foreign policy debacle, not least because of his unpredictable personality and penchant for antagonizing foreign leaders and publics. But they are wrong in asserting that he is somehow a danger to the traditional principles of the Republican Party. On the contrary, Mr. Trump represents a return to the party’s roots. It’s the neocons who are the interlopers.

The extent to which the neocons and their moralistic, crusading Wilsonian mission overtook the Republican foreign policy establishment, beginning in the 1970s, was so nearly complete that it can be hard to remember that a much different sensibility had previously governed the party, one reminiscent of Mr. Trump’s own positions: wariness about foreign intervention, championing of protectionist trade policies, a belief in the exercise of unilateral military power and a suspicion of global elites and institutions.

Consider the 1919 League of Nations debate, the crucible in which much Republican foreign policy was forged. In leading the charge against United States membership in entering the league, the Republican senator Henry Cabot Lodge argued that intervening abroad would undermine American security: “If you tangle her in the intrigues of Europe, you will destroy her power for good and endanger her very existence.”