In the 2004 and 2008 Democratic primaries, foreign policy was probably the most important topic of discussion. Since then, the subject has largely fallen by the wayside, as the population has stopped paying attention to the war in Afghanistan, and the dozens of other overseas interventions have been small enough (at least in terms of American casualties) to be easily overlooked.

However, this may change in 2020. Unlike in 2012, the economy is (fingers crossed) doing okay. And unlike in 2016, there is a major foreign policy question to draw everyone's attention — namely, how Trump has justified Saudi Arabia's butchering of a legal America resident, and how he has enabled an accelerating genocide in Yemen. It raises the question: Will the next Democratic nominee develop an alternative foreign policy to the neocon-lite imperialism that has dominated the party for over a decade?

Let's review some history. In 2004, the Democrats nominated John Kerry, a critic of the Iraq War who also voted for it. In 2008, they nominated Barack Obama over Hillary Clinton specifically because he did not support the war, but he proceeded to put Clinton in charge of the State Department and went on to conduct a foreign policy that only looks peaceable when compared to that of his predecessor, George W. Bush. Obama did push through the nuclear deal with Iran, but he also unleashed aggressive drone strikes, including the assassination of American citizens (including a 16-year-old boy) without any due process, and backed the Saudi war in Yemen for its first two years.

In the 2016 primary, Clinton's leftist challenger Bernie Sanders was palpably rusty on foreign policy at first, allowing one of his strongest angles of attack against her to lay fallow for months. She won, of course, making her probably the most belligerent Democratic nominee since Lyndon Johnson.

However, Sanders has considerably upped his game since then. During the campaign, he rapidly fleshed out a pretty solid foreign policy framework, and afterwards snapped up some key staffers. He's since delivered two major speeches, one outlining a basic foreign policy framework for the United States, and one advocating for a new progressive internationalism (with some help from former Greek Finance Minister Yanis Varoufakis). The idea clearly is to position Sanders as the candidate of peace, restraint, and calm international relations for 2020.

Elizabeth Warren, also positioning herself for 2020, has lately been trying to claim a bit of that ground herself. In a big speech last week, she outlined a foreign policy that would overhaul the broken international trade regime, wind down the war in Afghanistan, and stand up to the alliance of corrupt right-wing authoritarians. It's a bit of a change of tune for Warren, who used to sound very Clinton-esque on issues like Israel, and voted for Trump's defense bill last year, but on the whole it was a solid speech.

That brings me back to Yemen, Trump, and Saudi Arabia. The striking thing about the president's overt justification of the Saudis butchering American resident and Washington Post journalist Jamal Khashoggi is how perfectly it encapsulates the false picture of American "interests" that has dominated U.S. foreign policy for decades. After detailing the supposed huge investments Saudi Arabia is making in the U.S., and how they're keeping oil cheap, Trump insists that "America is pursuing its national interests."

Of course, Trump exaggerated the scope of Saudi investment by at least a factor of 30. But as Greg Sargent and Matt Yglesias argue, even aside from that hyperbole, his argument is an absolute crock. Just on a very cynical oil-for-alliance understanding of American interests, cheap Saudi gasoline is not so good when the president looks the other way when the failson dictator of that country murders American residents. Red-blooded patriots can't enjoy their Cadillac Escalades when they've been deposited in several different trash cans around Riyadh.

By a less cynical but more realistic view, cheap oil is bad because it harms American oil producers — who actually pump out more barrels than Saudi Arabia these days. By an even less cynical but more realistic still view, cheap oil is bad because it fuels climate change, which is going to severely harm the United States if it isn't stopped. And on purely moral grounds (which certainly is related to the national interest, if indirectly), murder is wrong.

Something similar is true for the genocidal Saudi war in Yemen. This conflict, which has already killed tens of thousands of people and is could kill millions more through famine and disease, is a strategic disaster for the U.S. Helping Saudi wedding- and schoolchildren-bombers with targeting and logistics (American forces were helping refuel them as well until recently, but they reportedly don't need that anymore), deeply implicates the United States with the worst humanitarian catastrophe in decades. It grossly harms our reputation, stokes furious hatred in the hearts of millions — oh, and Saudi Arabia is literally arming and paying al Qaeda as part of the effort — and for what? So a couple hundred defense contractors can have a third Jacuzzi in their McLean McMansions, and a couple hundred Saudi lickspittles at various suborned D.C. "think tanks" and lobbying shops can continue to collect their blood money salaries? No matter how you define it, that is not in the same galaxy as the national interest.

The question for 2020 is whether this will be much of a point of contention. Indeed, the Yemen disaster is so bad that Sanders teamed up with Sen. Mike Lee (R-Utah) to push through a bill ending all U.S. involvement in the conflict, which recently passed overwhelmingly. Still, the liberal imperialist wing of the Democratic Party is strong, which is probably why even Sanders and Warren have yet to lay out a really stark moral case for imperial rollback. But if Trump continues to enable the Yemen conflict, it may turn out that McGovern-style anti-imperialist politics will make a comeback. In any case, would-be 2020 contenders would be wise to develop a sensible, moral foreign policy platform.