Later, Republicans resisted Franklin D. Roosevelt’s efforts to gird the nation for war, passing legislation that limited rearmament and support for European allies. ~David Greenberg

Actually, FDR’s efforts to pull the U.S. into war were resisted because most Americans saw no need to involve the U.S. in it. To state the obvious, the U.S. did not have any European allies to support before the end of 1941, and we were certainly under no obligation to provide any support. Before entry into the war, the U.S. provided some support to countries at war with the Axis in spite of this.

I suppose it is true that isolationism, if it ever really existed, would “reject America’s leadership role in the world,” but it doesn’t follow that preferring that U.S. “leadership” be reduced or wound down is an isolationist position. One can favor quite extensive economic, cultural, and diplomatic engagement with the rest of the world without wishing to exercise “leadership” of the sort the U.S. has exercised since 1945, and one could even support a more modest form of that “leadership” without wishing “to actively manage world affairs.”

Before he demonstrated his poor understanding of the history of the 19th century, Marion Smith defined isolationism as “a coherent grand strategy composed of economic protectionism, military non-involvement, and cultural detachment.” This is a passable definition. Using this definition, we see that there is virtually no one on the left or right today who endorses such a strategy. This definition makes isolationism into something not very different from the pursuit of autarky. Obviously, neutrality is something very different, and it involves not becoming embroiled in foreign conflicts in which the U.S. has little or no stake.

Greenberg claims that “isolationism” is on the rise again “at a moment when the world needs America to play a stabilizing role.” It’s not at clear that the world needs this. What we do see is that many American hawks want America to play this role. At a time when this stabilizing role is probably less necessary than it has been in over half a century, we are being told that the U.S. cannot reduce its presence anywhere around the world.