John McCain’s recent efforts to smear Barack Obama as having a “Sept. 10 mind-set” is about more than making Democrats appear weak and out of touch when it comes to defending the United States’ national security. It is also an attempt to cloak the deep divisions among conservatives over the future direction of foreign policy.

Although Republicans were strongly unified after the Sept. 11, 2001, attacks, conservatism is breaking apart as the Bush administration comes to a close. Pragmatic realists are facing off against neoconservatives to dominate Republican Party foreign policy, while the lure of the two extremes of conservatism—isolationists skeptical of global engagement and nationalists defined mainly by their anti-immigration views—remains strong.

Such fissures are not new; in fact, they erupted nearly 20 years ago with the end of the Cold War. Anti-communism had been the glue that held the political right together for decades. In the wake of the fall of the Berlin Wall on Nov. 9, 1989, Republicans scattered among Pat Buchanan’s isolationism, the anti-Clinton nationalism of the “Contract With America” congressional Republicans, the realist pragmatism of establishment stalwarts such as James Baker and Brent Scowcroft, and neoconservative idealism. These factions endured throughout the 1990s and continued to battle one another when George W. Bush began his presidency.

Then came Sept. 11, and conservatives seized on Islamic terrorism as the new communism: an existential threat to the United States that could unify a diverse party and dominate the American national security debate.