After swerving with the headlines the past two years, the Republicans as a party better find some solid principled ground. In giving them majorities in both chambers, American voters will expect a responsible and mature GOP strategy for a world in turmoil.

Watch Mr. Cotton, whose 37 years belie a relatively well-formed worldview. His call for strong American leadership comes without bluster. He says he is willing to “nation-build” where “our national security interests become implicated.” He opposed the 2011 withdrawal from Iraq and wants the U.S. to stay on in Afghanistan, the two countries he knows well. “After World War II, we didn’t quit Germany and South Korea,” says Mr. Cotton.

Halifax is a good setting for a post-election gathering of would-be internationalists. The framers of future U.S. foreign policy might want to keep in mind the example of this so-called warden of the north, a major naval port for two centuries. During both world wars, the largest ship convoys to help allies in Europe left from Halifax. The Canadian city is a beating heart of Atlanticism. In the last century that was the faith in liberal democracies that stand up for each other, backed by strong militaries and U.S. leadership.