This article originally appeared in VICE US

On Friday, Nevada Republican senator Dean Heller announced that he was leaning against voting for the Senate healthcare bill being pushed by the GOP leadership. He wasn't the first Republican to provisionally come out against the bill, but the others were all uber-conservatives like Rand Paul and Ted Cruz who, many cynical observers figure, will eventually vote yes after the requisite yammering about their principles.

Heller's opposition is different. "I cannot support a piece of legislation that takes away insurance from tens of millions of Americans and hundreds of thousands of Nevadans," he said in a statement. In other words, he's against it for the same reasons many liberals and moderate Republicans are: The bill would pull the rug out from under too many people who depend on Barack Obama's Affordable Care Act for insurance.

The GOP can only afford to lose two Republican votes. And two moderates—Maine's Susan Collins and Alaska's Lisa Murkowski—have already signaled their skepticism, if not outright opposition. If they join Heller in forcing the bill to move to the left (by lessening the cuts to Medicaid, or keeping Planned Parenthood funded), it could derail the whole effort if conservatives refuse to compromise. At the very least, a Heller-Murkowski-Collins block could soften the bill, or simply stall its passage as negotiations take place.

It seems obvious that Heller has been pushed into this position by activists in Nevada. He's up for reelection this year, and his home state has a lot of people who want government to have a greater role in health care. At times, his office has been overwhelmed with calls demanding he break from Trump, he's been yelled at by constituents at town halls devoted to health care, he flipped his position on Planned Parenthood to say he'd defend it, and Democrats are openly talking about taking his seat.

He's been pressured, in other words, and it seems to be working. That was the message the ACLU, which opposes the Republican healthcare bill, was spreading Friday afternoon:

In the wake of announcing his opposition to the bill, a pro-Trump group has planned to target Heller in ads. Heller's also likely going to continue being deluged by Democratic activists who have promised to make his reelection a living hell if he votes for the bill. As anyone who's sat on a fence can tell you, it's an awkward position to be in. But as swing senators make their positions on the bill clear, Heller could emerge as the most important man in the chamber.