America’s political pundits have been uncomfortably confused by Donald Trump’s surge to lead the field of Republican presidential candidates. Now the Democrat candidate Bernie Sanders is presenting another head-scratcher, as he shows signs of presenting a legitimate challenge to frontrunner Hillary Clinton.

Sanders, a socialist from Vermont, is widely considered unelectable. But he overtook Clinton, the de facto Democratic presidential nominee, in a New Hampshire poll this week: 44% of those surveyed, all likely voters in the first nation’s first presidential primary in February, favored Sanders, while 37% favored Clinton. It was Sanders’s first time leading a poll in the 2016 race, and Clinton’s first time trailing in one.

On Aug. 9, two days before those poll numbers came out, Sanders attracted a crowd of 28,000 people at a rally in Portland, Oregon—the largest turnout for any candidate in this election cycle. On Aug. 10 in Los Angeles, he spoke to 27,000 people. By comparison, Clinton’s largest crowd totaled 5,500 people in New York.

Sanders is campaigning on his outsider credentials. And he is, as Molly Ball recently wrote in The Atlantic, “the most un-Clinton-like candidate there is—the nutty Vermont uncle of Democratic politics.”

Just like Republican voters seem to be doing with Trump, Democrats may be “dating” Sanders now without any intention of tying the knot. When the time comes to get practical—to choose a candidate that can actually win the national election in 2016—they’re still probably going to pick Clinton.

Unless, of course, vice president Joe Biden ends up running and then splits the practical vote.