For much of this year, the 2020 Democratic primary could have been fairly described as "Biden and Sanders and Their Single-Digit Friends," with the former vice president enjoying a comfortable cushion of somewhere between 20 and 30 points over his next-closest competitor. The results of an NBC News/Wall Street Journal poll released Tuesday, however, portray a very different race as the candidates head into the fall: Biden holds only a six-point lead over Massachusetts senator Elizabeth Warren, and there are telltale signs that the Warren-Biden gap could shrink even further in the months to come. The Summer of Warren, replete with its packed rallies and wonky proposals and hours-long selfie lines, is making a difference.

In addition to the standard who-would-you-pick-if-the-election-were-today question, the pollsters attempted to measure the relative strength of these preferences, too. Warren now commands the greatest percentage of Democratic primary voters—35 percent—who describe themselves as "enthusiastic" about her prospective general election candidacy. Just 25 percent and 23 percent of respondents said so about Biden and Sanders, respectively. These positions are a near-mirror image of survey results from six months ago, when 33 percent of voters were enthusiastic about Biden, compared to just 20 percent who felt the same way about Warren.

When the descriptor ratchets one notch down the excitement scale from "enthusiastic" to "comfortable," Warren fares just as well, at 35 percent. Sanders's number, however, increases to 37 percent, and Biden's spikes to 41. Towards the skeptical end of the feelings spectrum, 21 percent of voters say they still have "some reservations" or are "very uncomfortable" with Warren, compared to 35 percent and 37 percent who say the same about Biden and Sanders, respectively.

Put differently, Democratic voters would be fine with any of these three White House hopefuls trying to unseat Donald Trump next fall. But by a double-digit margin, it is Warren about whom they are most excited.

The poll also asked voters about their backup plans—which candidate they'd support if their preferred candidate were no longer an option. Here, again, Warren is the clear winner: 21 percent of respondents now say she's their second choice, compared to only 13 percent two months earlier. Sanders trails her by five points, followed by South Bend mayor Pete Buttigieg at 12 percent. Biden, the race's current leader, manages to poll at 11 percent in this category.