Their opposition took root early in Trump’s tenure. None of the 10 backed confirmation for Betsy DeVos as education secretary. Just Manchin, Heitkamp, and Donnelly voted to confirm Supreme Court Justice Neil Gorsuch. And, more recently, all 10 have signaled opposition to the evolving Senate Republican legislation to repeal the Affordable Care Act.

This pattern of resistance has forced Senate Republicans to try to squeeze more of their agenda into the reconciliation process, which requires fewer votes to pass legislation. It’s also framing what could be the pivotal question in next year’s Senate midterm elections: Will these Democrats pay a price for consistently opposing Trump in states that voted for him only last year?

“They had better hope the king is dead,” said Pennsylvania-based GOP consultant John Brabender, “and that a year from now Donald Trump isn’t being seen, on the core issues he promised to these [voters], that he has delivered.”

So far, though, both Casey and McCaskill—along with their colleagues—have been emboldened to oppose Trump precisely because they believe his agenda hasn’t met those voters’ needs. McCaskill said she “respects” Trump voters and their choice to “pull the pin on this grenade [to] see if we can upset the status quo.” But she argued that Trump’s agenda would deliver “a gut punch to [the] rural Missouri” communities where he ran best—thanks to a health-care plan that would raise premiums for older and small-town consumers; proposals to shift federal funding from public to private schools through vouchers; and an infrastructure plan centered on promoting private investment and adding toll roads, both of which are more likely to benefit urban areas.

Casey pointed to similar risks in the congressional GOP proposals to severely cut Medicaid, which he said could destabilize both the physical and economic health of rural Pennsylvania. (In over half of Pennsylvania’s rural counties, he pointedly noted, the local hospital is either the largest or second-largest employer.) Add in the toll-focused infrastructure plan and proposed reductions in community-development grants and home-heating assistance for low-income seniors, Casey said, and “I don’t think that’s what people in his base thought they were getting in their communities.”

Just as striking as the substance of the Trump 10’s criticism is its style. No one has ever used the word “firebrand” to describe Casey, a soft-spoken former state auditor with a centrist pedigree. (He’s one of the last prominent Democrats to oppose legal abortion.) Yet, since Trump’s victory, Casey’s defining image came when he rushed, still in formal white tie, from a Philadelphia Orchestra ball to join an airport protest against the president’s first travel ban in January.

“It’s not just the policy agenda, which I think … caters to the right,” Casey told me. “It’s the whole approach: the insults, the tweets, the dividing. … In most instances, presidents try to … be the adult in the room. [But] on many days … if there is not poison in the water, he tends to add the poison of division and discord instead of trying to bring people together.”