When the 20 Democratic presidential candidates take the debate stage Wednesday and Thursday, they’re likely to face at least a few questions about foreign policy.

After all, foreign policy is where a president has by far the most authority to act on their own, and where their decisions often have immediate life-or-death consequences for thousands if not millions of people.

It’s also one of the major areas where a chasm between the top Democratic candidates has started to show.

On one side are former Vice President Joe Biden and South Bend, Indiana, Mayor Pete Buttigieg, who believe in America’s traditional role as the guarantor of global security. On the other side are Sens. Bernie Sanders (I-VT) and Elizabeth Warren (D-MA), who want to throw out the old playbook and reform the global system.

“Biden and Buttigieg want to restore and reform the Obama-era legacy. Sanders and Warren look to go far beyond Obama by reshaping US foreign policy to remake global economic and political conditions,” says Paul Musgrave, an expert on US foreign policy at the University of Massachusetts at Amherst.

Few 2020 Democratic candidates have publicly discussed their foreign policy views yet, and those who have often leave out detailed specifics. But even at this early stage, a clear divide has begun to emerge among the frontrunners — a divide that will likely shape the Democratic foreign policy debate in the months to come.

This week American voters will get their first real chance to hear the main candidates discuss their policies back to back. Here are the key themes to listen for when it comes to foreign policy.

Biden and Buttigieg: the traditionalists

Since the end of World War II, Democrats and Republicans have pursued largely similar approaches to US foreign policy. Presidents from both parties have used US power to underwrite and maintain what’s called the “liberal international order,” which basically means the set of economic and political rules and values that help the world function.

The US never did this out of the goodness of its heart. Promoting free trade and liberal democracy was meant to provide America with markets to sell goods to and countries with which to build alliances against adversaries. It was never a perfect system, and the US made many, many errors along the way. But overall, that grand strategy helped the US maintain its position as the world’s preeminent power.

That, in a nutshell, is the world candidates like Biden and Buttigieg want to restore and protect.

“For the past seven decades, the choices we have made — particularly the United States and our allies in Europe — have steered our world down a clear path,” Biden said in a speech at the World Economic Forum in January 2017, just three days before leaving office.

“In recent years it has become evident that the consensus upholding this system is facing increasing pressures, from within and from without,” he continued. “It’s imperative that we act urgently to defend the liberal international order.”

Over two years later, Buttigieg offered a similar message. “The world needs an America ready to reverse the rise of authoritarianism while revitalizing democracy at home and advancing it among our allies,” the mayor said in a speech earlier this month.

While he acknowledged that it would not “be honest to promise that we can restore an old order that cannot, in any case, meet the realities of a new moment,” he nevertheless articulated a vision of American military and economic power as the principal guarantor of peace and stability around the world.

“Ironically, at the very moment when American prestige and respect is collapsing, it has never been more needed that America live up to the values we profess,” Buttigieg said. “The world needs the best of America right now.”

There are some differences between the two candidates’ views — Buttigieg has made progressive concerns like reforming American capitalism more central to his foreign policy than Biden has. He’s also struck a more adversarial tone against China than the former vice president Biden has, with the former vice president saying the country is “not competition for us.”

But on the whole, both candidates represent continuity with the American foreign policy tradition.

Sanders and Warren, however, represent change.

Sanders and Warren: the progressives

Both Sanders and Warren have made combating both domestic and global income inequality central to their foreign policies and argue that the liberal international order has failed the global middle class.

“There’s a story Americans like to tell ourselves about how we built a liberal international order — one based on democratic principles, committed to civil and human rights, accountable to citizens, bound by the rule of law, and focused on economic prosperity for all,” Warren wrote in Foreign Affairs last November. “It’s a good story, with deep roots ... [But] while international economic policies and trade deals have worked gloriously well for elites around the world, they have left working people discouraged and disaffected.”

That trend, they say, has not only hurt democracy in the US, but has also given rise to authoritarians from Europe to the Middle East to Asia. Progressive foreign-policy types like Sanders and Warren, then, want to change the global economic model to make everyday life better for working-class people, which they believe will in turn curb the rise of dictatorship and oligarchy.

“When we talk about foreign policy, and our belief in democracy, at the very top of our list of concerns is the need to revitalize American democracy to ensure that governmental decisions reflect the interests of a majority of our people, and not just the few — whether that few is Wall Street, the military industrial complex, or the fossil fuel industry,” Sanders said in a 2017 foreign policy speech.

Yet both candidates still agree with many elements of the “old” way. They both want to support and build up America’s alliances, for example, while propping up democratic forces around the world. They’re also not against American leadership (or the use of US military force) per se, but they do want it to work better for everyone. A Sanders or Warren administration, then, wouldn’t mean business as usual.

Some experts told me that these two competing sets of ideas are still too conceptual — that it’s nearly impossible to see a true split between the traditionalist and progressive camps unless and until the candidates provide more specifics. That’s a fair point. But even with the few details we do have, the ideological cracks have started to show.