The wild card may be how voters react to a growing demand among Democrats for a single-payer, government-run health care system. Mr. Sanders has proposed legislation to create that kind of health care system, and scores of Democratic candidates have endorsed the idea.
Senator Tammy Baldwin, Democrat of Wisconsin, wrote an op-ed last year titled: “Why I support Medicare for all and other efforts to expand health coverage.”
Several other Democratic senators, including some who are weighing a run for president in 2020, have backed the idea, though Democratic candidates running in conservative states like West Virginia, Indiana and North Carolina have distanced themselves from that approach.
And last week, former President Barack Obama for the first time embraced the idea of “Medicare for all,” saying in a speech that it was one of the “new ideas” that was powering Democratic candidates to success across the country. In the past, Mr. Obama had dismissed the notion, saying that most Americans were satisfied with the employer-based system of private insurance.
In Montana, Mr. Trump presented an apocalyptic vision of what extending Medicare would look like. “They’re going to ruin your Medicare. Watch. They want to turn America into Venezuela. I don’t think so,” he said, prompting boos from the audience. “Democrats would destroy Medicare with ‘Medicare for all’ — you heard that — ‘Medicare for all,’ until they run out of money, which would be like in the third day.”
Republicans point to a study suggesting that a “Medicare for all” program could cost $32 trillion over a decade. The Republican National Committee echoed Mr. Trump’s message in an email to reporters on Tuesday: “Under Democrats’ Dream of a Single-Payer Health Care System, Medicare Recipients Would Lose Out on Quality and Coverage,” the email asserted.
In Maine, the Republican House incumbent has begun airing a campaign ad that accuses Jared Golden, his Democratic opponent, of supporting “a risky scheme” to end Medicare. Mr. Golden’s campaign called the ad “a desperate attack” with no merit.