Over the past two weeks, the American foreign-policy debate has dramatically changed. The key to understanding why lies in a book.

The book is called Special Providence. Published 13 years ago by Walter Russell Mead, it remains, for my money, the best analysis of American foreign policy written in our time. Mead argues that America has four foreign-policy traditions. He calls the first “Wilsonianism.” It represents America’s missionary desire to spread civilization across the globe. Once upon a time, spreading “civilization” meant spreading Christianity. Now it means spreading democracy and human rights. Samantha Power is a Wilsonian. 

The second tradition is “Hamiltonianism.” It refers to the belief that America, as a trading nation separated from our largest markets by vast oceans, must make the world safe for American commerce. For our domestic prosperity, we must maintain an economically open, politically stable world order. George H.W. Bush is a Hamiltonian. 

The third is “Jeffersonianism.” It reflects a deep-seated fear that if America entangles itself in imperial ventures abroad, we will destroy liberty at home. Glenn Greenwald and Ron Paul are Jeffersonians. 

The fourth—and for our purposes most relevant—is “Jacksonianism.” It refers to the peculiar combination of jingoism and isolationism forged on the American frontier. Bill O’Reilly is a Jacksonian. Jacksonians don’t want to fashion other countries in America’s image. They don’t care about fattening corporate bottom lines. But if you mess with them—violate their honor—they’ll pursue you to the gates of hell.

If that phrase sounds familiar, it’s because Joe Biden uttered it on Wednesday about the Islamic State of Iraq and Syria (ISIS). He said it, I suspect, in part because he recognizes that over the last two weeks, America’s foreign-policy debate has turned Jacksonian in a way that could cause the Obama administration a great deal of trouble.

I’m not talking about the elite debate. Foreign-policy elites began growing more hawkish almost a year ago, after Barack Obama abandoned his plans to bomb Syria for using chemical weapons and Russia swallowed Crimea. But until recently, those elite criticisms enjoyed little public traction. That’s because, in Mead’s terminology, they were largely Wilsonian and Hamiltonian. Wilsonians were upset about Bashar al-Assad’s human-rights violations and Russia’s offenses against international law. Hamiltonians feared that unless America acted forcefully, our declining credibility would undermine world order. 

But Wilsonianism and Hamiltonianism are largely elite traditions, and the public was unmoved. When Obama asked Congress to support military strikes against Assad last fall, the public overwhelmingly said no. For all the denunciations of Obama’s Ukraine policy this summer by Beltway hawks, Republican congressional candidates barely mentioned it. Up until very recently, public opinion was strongly “Jeffersonian.” Americans generally told pollsters that their government was too militarily entangled overseas already. 

The beheadings of James Foley and Steven Sotloff have changed that. Republican Senate candidates in Alaska, Georgia, and New Hampshire are now tying their Democratic opponents to Obama’s supposed lack of a strategy against ISIS. Democratic Senators Bill Nelson and Tim Kaine are urging Congress to authorize the president to bomb the Sunni extremist group in Syria and Iraq. Last September, when YouGov.com asked Americans whether they supported air strikes “against Syria,” only 20 percent said yes. Last week, by contrast, when it asked whether Americans supported strikes “against ISIS militants in Syria,” 63 percent said yes.