ANALYSIS: Democratic Debate Takes Fiery Turn, But Stays on Substance

— -- The race for the Democratic nomination may be effectively over, or at least well on its way. But the populist fire that's being stoked by Bernie Sanders' campaign isn't dying down -– at least if Sanders has anything to do with it.

On a night that he notched another caucus win, Sanders used Michigan as a backdrop Sunday for a renewed and refreshed attack on Hillary Clinton. He hit her for supporting trade deals and corporate welfare, for speeches to big banks and supporting a super PAC, amid a series of now-familiar fault lines that somehow took on new urgency.

"If you are talking about the Wall Street bailout where some of your friends destroyed this economy..." Sanders began, only for Clinton to try to jump in.

"Excuse me, I'm talking," Sanders said.

"If you are going to talk, tell the whole story, Sen. Sanders," Clinton responded.

"I will tell my story and you tell yours," he shot back.

That they are doing, and will continue to do, even with the true drama of the campaign on the other side of the aisle.

"Excuse me, I’m talking" would count as one of the friendlier rejoinders had it come during a debate on the Republican side. But the sharpness matters for the Democrats –- and could be a dynamic that the party is happy to see last a while longer.

From the start, the debate in Flint was a chance for the two Democrats to respond to the tragic circumstances surrounding the city's water supply. Clinton joined Sanders in calling for Michigan's Republican governor, Rick Snyder, to resign, and both went deep in addressing a topic their GOP rivals have barely touched.

When the debate moved to areas where the Democrats actually disagree –- trade, gun control, Wall Street -– Clinton and Sanders engaged with each other fully.

"Let's have some facts instead of rhetoric for a change," Clinton said when Sanders attacked her over her super PAC and paid speeches to Wall Street banks.

Clinton has taken to calling Sanders a "one-issue candidate" – and Sanders accepted the label.

"Secretary Clinton said I'm a one-issue person. I guess so. My issue is trying to rebuild a disappearing middle class," Sanders said.

Remarkably, for two veteran politicians who have now shared a stage seven times -– and will see each other again, in Miami, in just three days -– the lines between Sanders and Clinton don't seem stale. They found plenty of reasons to agree with each other, in the safe territory of contrasting themselves with the GOP contenders.

"Compare the substance of this debate with what you saw on the Republican stage last week," Clinton said.

"We are, if elected president, going to invest a lot of money into mental health," said Sanders. "And if you watch the Republican debates, you know why."

Clinton and Sanders have kept the campaign about substance, for the most part, even if the same ground has been tread repeatedly. Given the noise being generated by the GOP these days, the passion on the Democratic side may be a welcome dynamic.