Or consider the famously isolationist Sen. Robert Taft (R-Ohio), a role model of former Rep. Ron Paul (R-Texas). As a presidential candidate, Paul routinely touted Taft's opposition to U.S. membership to NATO as proof of the GOP's isolationist roots. But Taft also supported the Truman Doctrine and, albeit reluctantly, the Marshall Plan. He promised "100 percent support for the Chinese National government on Formosa [Taiwan]," and wanted to station up to six divisions in Europe. What an isolationist!
Meanwhile, countless leading liberals and Democrats embraced isolationism by name in the 1930s and by deed after World War II. J.T. Flynn, the foremost spokesman for the America First Committee, for example, was a longtime columnist for the liberal New Republic.
The self-avowed isolationist movement died in the ashes of World War II. But while it lived, it was a bipartisan cause just like interventionism. Similarly, the competing impulses to engage the world and to draw back from it aren't the exclusive provenance of a single party; rather they run straight through the American heart. And neither impulse is always right for every challenge. Even most hawks preferred a cold war to a hot one with the Soviet Union. And most doves supported striking back against al-Qaeda after 9/11.
Many supposedly isolationist libertarians are for free trade and easy immigration but also want to shrink the military. Many supposedly isolationist progressives hate free trade and globalization but love the United Nations and international treaties.
Krauthammer is absolutely right that the GOP is going to have a big foreign policy debate -- and it should (as should the Democrats). I'm just not sure bandying around the I-word will improve or illuminate that debate very much.