Last night's Democratic debate in Miami was a welcome reprieve from the increasingly unhinged, vulgar, and mean-spirited GOP contests that receive such lavish attention from the political press. It prominently featured issues of particular concern to Latinos and Hispanics—above all immigration—as the Florida primary looms. And Bernie Sanders won.

Part of the reason Sanders helped his campaign last night was circumstantial. The focus on immigration meant that foreign policy questions, an area in which Sanders hasn't excelled in the debates, weren't really a part of the conversation. (I'm not counting the detours into U.S. policy toward Central America in the 1980s, and questions about Cuba.) The moderators also seemed to ask Clinton more pointed, difficult questions than they did Sanders. She was on the defensive for much of the evening, and deprived of the opportunity to emphasize her experience as Secretary of State and knowledge of world affairs. The basic frame of the debate, then, played to his strengths.

But tonight it also was clear the challenges Clinton faces in effectively criticizing Sanders. One of his greatest political liabilities remains the ambition of his domestic agenda. Clinton's difficult task is to deflate the hopes stirred by Sanders's rhetoric without seeming hostile to his broad aims, which are shared by many in the Democratic Party. It's not always gone well; an exceedingly peculiar declaration from Clinton in late January is just one example, when she drew raucus applause at a rally for celebrating that universal healthcare "will never, ever come to pass."

Clinton's attacks on Sanders, especially on the domestic front, tend to take two main forms: charging that his plans are those of an impractical dreamer, and seizing—often in distorting ways—on those votes or statements of his that give her the rare chance to knock him from the left. The latter marked her approach last night. To take one example, Clinton claimed Sanders was against the auto industry bailout, an accusation that's not true, at least not in the way she wants it to be. Sanders supported such a bailout in December 2008, but then, in early 2009, did not vote to disperse a second round of TARP money—most of it was channeled to financial institutions, but a much smaller amount went to the auto industry. Sanders's objection was to TARP, not a bailout for Detroit. David Axelrod has called Hillary's assertion a "cheap shot," and, given Sanders's victory in Michigan, it hasn't seemed to make a difference. Even the editorial board of the New York Times lamented Clinton's "negative tactics," writing that they've "hurt her credibility."

Finding a way to draw contrasts is even more difficult when the substantive differences between the candidates is as minimal as it is on immigration. Both Sanders and Clinton favor comprehensive immigration reform. Both disagree with President Obama on his approach to deporting undocumented immigrants. The moderators extracted significant concessions from both candidates, too, with Sanders and Clinton pledging not to deport undocumented immigrants who haven't committed violent crimes. But here again, Clinton couldn't resist the low blow, arguing that Sanders "stood with the Minutemen vigilantes in their ridiculous, absurd efforts to, quote, 'hunt down immigrants.'" (This refers to an amendment Sanders voted for that prevented the U.S. government from providing information about the Minutemen and other groups to foreign governments.)

In another odd attack, Clinton claimed that Sanders was an ally of the Koch brothers, because they agree with his opposition to the reauthorization of the Export-Import Bank and ran an ad praising him for that stance. Obviously, Sanders has almost nothing in common with the billionaire libertarians, and this simply was an instance of principled libertarian opposition to corporate welfare tracking with similar opposition from the left.

These examples are illustrative of why the debate went so well for Sanders. It only makes Clinton look bad when she seriously tries to convince the audience that Sanders is pro-vigilante justice on the Mexican-American border, that he "stood with" the Minutemen as a friend and ally, supportive of their aims. It only looks like a reach when Clinton, who again and again hits the profligacy and irresponsibility of the socialist from Vermont's plans, portrays him as begruding a few billion dollars for the auto industry—especially when you consider Sanders's strong support for trade policies aimed at keeping manufacturing jobs in the U.S. And it not only is a reach, but simply beggars belief, for Clinton to suggest the socialist Sanders actually is of a piece with the libertarian Kochs. Fairly or not, Clinton struggles to convince voters of her honesty and trustworthiness. Attacks like those she made last night don't help. They weren't just tactical mistakes or the usual stretching of the political truth; they were, at their worst, absurd.

This not to say Sanders never faltered; his longstanding posture of openness and even sympathy for the communist government in Cuba will not help him with Cuban voters in Florida. And of course Clinton, for the most part, was steady and informed. But on a night when Sanders was sharper than usual, and in which the topics and themes suited him, Clinton's ill-conceived slanders only served to remind viewers of her worst instincts and tendencies. 

At the end of the debate, as Sanders finished his closing remarks, the debate audience offered him a standing ovation. The way forward remains difficult for him; but last night, at least, he received the applause he deserves.