All aboard the Dean Phillips Express!

An eagle-eyed motorist spotted a campaign bus devoted to the Democratic congressman from Minnesota, who is preparing a belated primary challenge to President Biden after spending months bemoaning the lack of internal opponents to the 80-year-old commander-in-chief.

Longtime Twin Cities reporter Jason DeRusha tweeted a picture Tuesday morning of the Dean Phillips for President bus, which he said was sent to him by a friend from the road in Ohio.

“Bus says ‘Make America Affordable Again’ and uses [Phillips’] slogan ‘Everyone’s Invited!'” tweeted DeRusha, who added that a Phillips campaign website was registered Oct. 12, though it has not yet gone live.

Politico reported late last week that Phillips, 54, was expected to declare his candidacy this coming Friday, the deadline for candidates to file for the New Hampshire primary.

A Post inquiry to a Phillips spokesperson Tuesday was forwarded “to the campaign,” which did not immediately respond.

Phillips’ apparent emphasis on New Hampshire recalls the strategy of another Minnesotan, Sen. Gene McCarthy, who nearly upset President Lyndon Johnson in the 1968 Granite State primary running on an anti-Vietnam War platform. McCarthy’s strong showing triggered a series of events, including the candidacy of Sen. Robert F. Kennedy, that led Johnson to decide not to seek a second full term.

While Phillips has been a reliable vote in Congress for the administration’s policies, he stepped down from the House Democratic Policy and Communications Committee earlier this month in apparent preparation for announcing his run.

“My convictions relative to the 2024 presidential race are incongruent with the majority of my caucus, and I felt it appropriate to step aside from elected leadership to avoid unnecessary distractions during a critical time for our country,” Phillips said at the time.

Phillips has previously said that Biden should not run for a second term, telling CBS’ “Face the Nation” in August that “Democrats are telling me that they want, not a coronation, but they want a competition.”

“If we don’t heed that call, shame on us,” Phillips added. “And the consequences, I believe, are going to be disastrous. So, my call is to those who are well-positioned, well-prepared, of good character and competency, they know who they are, to jump in because Democrats and the country need competition. It makes everything better. That’s my call to them right now.”

Currently, Biden’s only challenger for the Democratic nomination is self-help author and spiritual guru Marianne Williamson. The RealClearPolitics polling average shows Biden getting 70.3% support nationwide, with Williamson at an even 9%.

A pair of polls released last week by Quinnipiac University and CNBC put Biden’s job disapproval rating at 56% and 58%, respectively, among US adults.

Meanwhile, a CNN/SSRS poll taken in late August found 67% of registered Democrats and Democrat-leaners think the party should choose a different candidate for president next year.