The Republican Party once won elections on national security. Back in 2004, incumbent George W. Bush maligned his Democrat opponent John Kerry as a weak "flip-flopper" on the Iraq war, convincing voters that the Republican ticket would lead America decisively during the "war on terror."

But after more than a decade of war, Americans have become increasingly critical of Bush-era foreign policy decisions. According to the pollster Gallup, 53 percent of Americans now believe the Iraq war was a mistake. And although 66 percent of Republicans still stand by the invasion, nearly a third of the party now regrets the misadventure.

"There really is a kind of international commitment fatigue among the general public and that includes a lot of Republicans," Colin Dueck, the author of Hard Line: The Republican Party and US Foreign Policy since World War II, told DW. "It's just simply the case the people are in no mood in this country for further military interventions overseas."