A bipartisan group of 10 governors wrote a letter Wednesday urging the Senate to reject a proposed “skinny” health care bill that Republican leaders are now trying feverishly to pass. And if the collective voice of so many governors doesn’t get the attention of GOP leaders, the letter’s endorsement by one particular Republican governor might.

It’s Brian Sandoval, from Nevada. He has emerged as a key player in the health care debate because GOP leaders in Washington desperately need the vote of Nevada’s Republican senator, Dean Heller.

Heller’s opposition alone could very well sink legislation, given that two out of the Senate’s 52 Republicans have already said they would oppose any Obamacare repeal option now under official discussion. And Heller has said he will listen closely to what Sandoval advises.

“If you want my support … you better make sure that the Republican governors that have expanded Medicaid sign off on it,” Heller said in a June press conference, at which he appeared alongside Sandoval. “I’ve been saying that for months. … Where is Governor Sandoval? What does he think?”

It’s a pressing question, because the Senate is on track to vote on a repeal bill by week’s end, and the focus of GOP leaders has shifted. Having failed so far to find a majority that would support a sweeping repeal effort, the leaders are now talking about passing a much narrower measure that, at least on paper, would do very little except eliminate the Affordable Care Act’s individual mandate.

The strategic theory of the skinny bill is that the individual mandate, which fines people who decline to get insurance, is among the most unpopular provisions in Obamacare. Folding its elimination into a bill that also repeals the employer mandate and device tax, but leaves out contentious issues like cutting Medicaid or changing the rules for private insurance, would supposedly be an easier vote for all Republicans.

Once such a bill got through the Senate, the argument goes, Majority Leader Mitch McConnell (R-Ky.) and his allies could start negotiating with their counterparts in the House, which passed a broader reform bill in May, to hash out a compromise that could eventually pass both chambers.

Heller is among the key Republican senators who have already indicated they’re inclined to support such a measure, as long as it doesn’t touch Medicaid. But critics have warned Heller and other Republicans that nothing would prevent House and Senate leaders from adding Medicaid cuts in their negotiations. And even if the skinny bill were to become law as is, without additional Medicaid provisions, it would pose a danger to the private insurance market simply by eliminating the individual mandate.

The mandate pushes healthy people to buy coverage, thereby making it possible for insurers to offer coverage to anybody with pre-existing conditions. Without it, insurers would likely jack up rates above and beyond where they would already be ― a possibility the governors raised explicitly in the letter.

“The Senate should also reject efforts to amend the bill into a ‘skinny repeal,’ which is expected to accelerate health plans leaving the individual market, increase premiums, and result in fewer Americans having access to coverage,” says the letter, which Louisiana Gov. John Bel Edwards (D), Ohio Gov. John Kasich (R) and Pennsylvania Gov. Tom Wolf (D) also signed.

Passing a skinny bill could actually affect premiums as early as next year, even if Senate leaders don’t envision it becoming law, because insurers must finalize rates within the next few weeks. They might raise rates pre-emptively ― just in case House-Senate negotiations prove fruitless and Republicans end up enacting the law because it is their only way to pass something they can call “repeal.”

One GOP senator, Rand Paul of Kentucky , is already suggesting that enacting the skinny bill without amendment might be the best possible outcome.

As it is, plenty of insurers are nervous because the Trump administration has started cutting funds for efforts to help enrollment ― and because the administration has signaled it might stop paying crucial, legally contested payments to insurers.

“Policy analysts debate how much the mandate is actually impacting enrollment, but plans will price as though repeal of the mandate drives adverse selection,” Caroline Pearson, senior vice president at Avalere consulting, told HuffPost. “So, passing a skinny repeal bill that repeals the mandate would directly increase premiums for the following year.”