In the Democratic presidential candidates' fourth debate Sunday, Sen. Bernie Sanders (Vt.) and former secretary of state Hillary Clinton wasted no time getting into it on health care.

The two went back and forth about whether Sanders's universal health-care plan, which he released hours before the debate and which essentially would provide Medicare for all Americans, is realistic.

Clinton said his plan would amount to tearing up the Affordable Care Act and starting over from scratch -- dividing the country. She added that it would be unlikely to get through a Congress that will have one Republican chamber, if not two, come 2017. Sanders retorted that Americans can't afford not to adopt his plan, and he largely avoided the politics of how he'd get it done.

"Right now, what we have to deal with is the fact that 29 million Americans still have no health insurance," he said.

Their most recent spat underscores the central division between the two candidates: Sanders is the candidate of grand proposals and political revolution -- a word he spoke repeatedly Sunday night -- while Clinton is more focused on pragmatism and building on what President Obama has already done.

In other words, Clinton is the candidate who is more realistic about what can be accomplished in today's divided political landscape. Sanders is aiming for more progressive ideas that would be much tougher to pass and implement -- if not downright impossible, such as single-payer health care.

If you're a Democratic primary voter, Sanders's candidacy is arguably more exciting. And the issue of health care is no exception. While Obamacare has a 67 percent approval rating among Democrats, December polling from the the Kaiser Family Foundation shows 76 percent of Democrats strongly or somewhat favor the general idea of universal health care.

But that -- and the majority of policies that form the center of Sanders's platform -- have almost no chance getting through Congress in the near future. Which party controls the Senate could change in November, but come Inauguration Day 2017, the House will almost certainly will be under Republican control.

That would make it nearly impossible for a President Sanders to switch the nation's health-care system into a government-controlled one that is anathema to Republicans' free-market views. With Democrats in charge of the House and the Senate in 2009 and 2010, Obama and his allies fought tooth and nail to pass his reforms to the private health-care system. As Clinton pointed out Sunday, a proposal to move to the kind of single-payer system Sanders favors was so politically divisive, it didn't even come up for a vote.

The question we keep asking ourselves is: Do Sanders supporters care that their guy's ideas would be dead on arrival in a Republican Congress? As he inches closer and closer to Clinton in both national and early-state polling, you could reasonably argue that they don't.

That could change, of course. With her lead threatened, Clinton has only recently started regularly attacking Sanders. Her attempt to bat down hopes about his universal health-care plan becoming law was one of her most forceful arguments against his candidacy. (For what it's worth, Clinton sought to emphasize less that what Sanders wants to do is unworkable and more that it would undo Obamacare -- and by extension undermine Obama himself.)

But being the voice of reason in this polarized election cycle isn't easy. Just ask Jeb Bush.

As we've argued before on The Fix, the decision among Democratic primary voters could come down to head vs. heart.

We'll end by noting that beyond the politics in Washington, Sanders has another roadblock to his ambitious agenda: That same Kaiser poll shows that just 5 percent of Democratic voters would make universal health care their top voting issue.

That's not good news for Sanders, because to make his proposals a reality, he's is going to need all the help he can get.