A longtime moderate, the Democratic congressman now says he had been “convinced through propaganda” that calls for universal health care were “a nonsensical leftist notion.”As he mounts a long-shot primary challenge to President Biden, Representative Dean Phillips says he has had an epiphany about American health care policy.Gone is his yearslong skepticism about adopting a national single-payer health care system. Now Mr. Phillips, a moderate Democrat from Minnesota, is embracing the “Medicare for all” proposal championed in two presidential campaigns by Senator Bernie Sanders — whose former top aide is now advising Mr. Phillips’s campaign.Mr. Phillips said in an interview on Tuesday that he would join as a co-sponsor to a House proposal that would expand Medicare by creating a national health insurance program available to all Americans, a shift that comes seven weeks into a presidential campaign that has yet to show significant progress in public polling.“I was a good example of someone who had been convinced through propaganda that it was a nonsensical leftist notion,” Mr. Phillips said. “It’s not. It really isn’t. And that’s I think that’s part of my migration, if you will, a migration of understanding and due diligence and intellectual curiosity and most importantly, listening to people.”Embracing the House bill is a low-stakes maneuver. With Republicans in control of the chamber, there is little chance it will come to a vote. Even when Representative Nancy Pelosi of California was speaker, Democrats never held a vote on proposals for Medicare for all that were championed by their progressive caucus — largely because President Biden didn’t support such a move, and centrist Democrats believed it was a bridge too far.Mr. Phillips — who spoke in the interview by videoconference, from an onscreen profile identifying him as “Generic Democrat” in a sly nod to the party’s best performer in polls — argued that his recent evolution on health care was not an effort to outflank Mr. Biden from the left.Instead, he said, he has become convinced that expanding Medicare, the government-run insurance program for older people, to cover all Americans would end up saving the federal government money and should attract support not just from progressives but also from conservatives — including backers of former President Donald J. Trump.“This is not a Hail Mary, by any stretch,” Mr. Phillips said. “It’s not an olive branch to progressives. You know what it really is? It’s an invitation to Trumpers.”Mr. Biden’s campaign spokesman, Kevin Munoz, declined to comment about Mr. Phillips.Mr. Phillips, a businessman who grew wealthy helping to run his family’s liquor distilling empire and later helped build a gelato behemoth, is a former board chairman of Allina Health, one of Minnesota’s largest health care systems. He said his beliefs began to change about 10 years ago, when his daughter Pia, then 13, received a diagnosis of Hodgkin’s lymphoma, and he saw “the gaps between the haves and the have-nots.”In July 2020, as a first-term congressman, he embraced a “state public option” that would allow Americans to buy into Medicaid. More recently, he said, he has been consulting with Representative Pramila Jayapal of Washington, the chair of the Congressional Progressive Caucus, who is a lead sponsor of the House Medicare for all bill, backed by more than half of House Democrats.Mr. Biden has moved the Democratic conversation about health care away from the idea of a single-payer plan, focusing instead on narrower issues like lowering drug costs and improving maternal health.“This is not a serious proposal in today’s environment,” Leslie Dach, the chair of the health advocacy group Protect Our Care and a former Obama administration official, said of Mr. Phillips’s switch. “We’re living in an era where it takes all of our energy to protect what we have from Republicans in Congress.” Mr. Phillips has not gained much traction. A poll last month from CNN and the University of New Hampshire found that he had support from about 10 percent of likely Democratic primary voters in New Hampshire, the only state where he has a campaign apparatus. Mr. Biden’s name will not be on the ballot there, but the same CNN poll found that 65 percent of voters said they would write in his name.Mr. Phillips said he hoped to do well in New Hampshire before moving on to Michigan, where Mr. Biden’s approval ratings in recent polls have taken a hit from Black and Arab American voters who disapprove of his support for Israel in its war against Hamas.But Mr. Phillips offered little in the way of daylight between himself and Mr. Biden on that conflict, which has left Democratic voters fiercely divided. The congressman said that he would not call for an immediate cease-fire and that he did not consider Israel “an apartheid state,” as many on the left argue.Yet Mr. Phillips contended that Democrats were so disenchanted with Mr. Biden that when presented with another option, they would take it. “The good news is that 66 percent of the country does not yet hate me,” Mr. Phillips said, in a dig at the president’s dismal approval ratings. “America has already made up its mind about President Biden and Vice President Harris.”