Bernie Sanders has the most to gain at the first debate. Here's how he could win it.

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The pressure is on for Bernie Sanders. While the first Democratic presidential debate presents the socialist senator from Vermont with an opportunity to ride a tide of grassroots support into the mainstream, his success hinges on whether he can make a good first impression, Politico reports. And if he fails to do so, his now-surging campaign could face the consequences:

"This is an opportunity for him to introduce himself to a much broader part of the country, so it's important for him to explain where he comes from, who he is," explained top Sanders strategist Tad Devine, adding that the senator had prepared to discuss areas where he disagrees with Clinton, from Syria to college affordability.Yet it's precisely because of his chance to introduce himself that Sanders has little room for error: he can't afford to make a bad first impression on a wide swath of Democratic voters in the states beyond his own Vermont and New Hampshire, where he leads Clinton. [Politico]

If Sanders emerges victorious tonight, successfully imprinting a friendly, lasting impression on the American public, his unexpected gains on Clinton in the polls could continue to creep up. But if he doesn't, his reputation as nothing more than a "fad" could be solidified. Bernie only has one chance.