WASHINGTON — Underdog Democratic presidential candidate Bernie Sanders is winning fans on the campaign trail — by flying coach.

Supporters of the rumpled Vermont senator have taken to posting snaps of Sanders crammed in among his fellow travelers as he jets across the country in his uphill effort to defeat Democratic front-runner Hillary Clinton.

A stream of images are posted under the hashtag #SandersOnAPlane — including one showing the Brooklyn native sneaking in some computer time while sitting between two passengers.

“I’m voting for the guy willing to sit in the middle seat,” wrote one admirer in an image that has been widely shared.

It’s an unmistakable contrast with Clinton, who has taken heat this election cycle for taking trips on Gulfstream jets and for banking millions on the speaking circuit.

Jennifer Rogers, 32, of Oklahoma, recalled sitting next to Sanders on a Southwest flight: “It’s awesome he flies with the citizens rather than a private jet,” she said.