WASHINGTON — Today Hillary Clinton’s former Democratic primary rival Bernie Sanders will stump in New Hampshire on Clinton’s behalf, kicking off the final, post-Labor Day stretch of the election season.

But a question remains: Will the seemingly reluctant surrogate muster enough enthusiasm for Clinton — and not just against her Republican rival — to convince the progressive millennials that flocked to him to now embrace the former secretary of state?

Sanders will speak this afternoon at a rally at Lebanon High School about Clinton’s plan for the economy, an issue upon which Sanders’ own presidential bid was strongly focused.

But in the time since Sanders endorsed Clinton during the lead-up to the Democratic National Convention in July, he has not exactly been a full-throated Clinton cheerleader.

While President Obama and Vice President Joe Biden have already campaigned fervently for Clinton — and will continue to do so though October — today marks the very first Clinton campaign trail appearance for the Vermont senator.

In interviews, his embrace seems far from warm.

“This is not about Trump, it’s not about Clinton, it’s about the American people,” Sanders said yesterday on NBC’s “Meet the Press,” pointing out that voters are concerned about jobs, climate change, rebuilding the nation’s infrastructure and passing immigration reform.

He added, carefully, in a sentence packed with modifying clauses, “On all of those issues, to my mind Hillary Clinton is far and away the superior candidate. And I hope people see that.”

Clinton needs Sanders’ backers, as several national polls put her in a virtual dead heat with Trump. The tightness of the race just two months before the election underscores the need for Clinton to bolster her support among the millennials who felt the Bern.

An NBC/Wall Street Journal poll shows nearly a third of millennials are disillusioned with both presidential front-runners, saying that they plan to vote for either Green Party candidate Jill Stein or Libertarian nominee and former New Mexico Gov. Gary Johnson. Many of those under-34 voters previously supported Sanders.

Asked how to woo those voters to Clinton’s side, Sanders said: “Hillary Clinton or Donald Trump is going to become president of the United States and there is no question to my mind that Hillary Clinton is far, far, far and away the superior candidate.”

Still not exactly a ringing endorsement, but the Clinton campaign is banking on it being enough.