The failure — so far, anyway — of Senate Republicans to concoct a health care proposal that could win the necessary 50 votes from the 52-member GOP Senate caucus must have proven particularly agonizing for Sen. Dean Heller (R-NV). The endangered senator, who is the only Republican from a state that Hillary Clinton carried facing reelection in 2018, ended up voting for the so-called “skinny repeal,” which would have rolled back the Affordable Care Act’s individual and employer mandates (that’s the one that Republican Sens. Susan Collins of Maine, John McCain of Arizona, and Lisa Murkowski of Alaska killed), but Heller did not support other proposals that would have scaled back the ACA’s Medicaid expansion.

Depending on the salience of health care next year, Heller could find himself in a tricky spot. Democrats will be enthused to vote against him no matter what, but he also could lose a very small but significant number of President Trump supporters because of his health care triangulation. Something similar arguably happened to former Rep. Joe Heck (R, NV-3), who lost a competitive Silver State Senate race to now-Sen. Catherine Cortez Masto (D-NV) last year. Both Heck and Trump lost Nevada by almost identical margins (about 2.5 points), but their patterns of support were a little bit different. Heck actually captured by less than a point the typically-vital swing county Washoe, home to Reno, while Trump lost it by less than a point. However, Heck ran a little bit behind Trump in some very Republican counties that make up the non-Las Vegas and Reno parts of the state. Heck seemed like the kind of candidate who could run ahead of Trump statewide, but his dis-endorsement of Trump after the emergence of the infamous Access Hollywood audio in October 2016 may have ended up costing him some crucial support. It’s possible that Heller could face a similar problem, although it’s far too soon to know.

Heller’s path to victory is maximizing his vote in the very Republican rural counties, clearly winning Washoe, and holding the Democratic candidate to a single-digit victory in Clark County, home to Las Vegas and where about two-thirds of the vote will be cast. That’s generally how Heller, then an appointed senator, narrowly won in 2012 over then-Rep. Shelley Berkley (D, NV-1), whose ethical problems made her a below-average candidate.

The White House is not happy with Heller, as demonstrated most notably by Trump’s seeming threat to Heller while the senator was sitting next to him (“And he wants to remain a senator, doesn’t he?”). It’s possible that Heller will face a primary challenge, perhaps from perennial candidate Danny Tarkanian (R), who most recently came up just short against now-Rep. Jacky Rosen (D, NV-3) last year.

Speaking of Rosen, the first-term House member is now challenging Heller in the Senate race, giving Democrats a credible if somewhat green candidate against the incumbent. Harry Reid, the former Democratic Senate leader, is still deeply involved in Silver State politics, and his machine is behind Rosen. Rep. Dina Titus (D, NV-1) is also a possible candidate, and she and Reid have a rocky relationship. Both sides hope primaries distract the opposite party’s current nomination frontrunners, Heller and Rosen.

We are moving Nevada from Leans Republican to Toss-up because of Heller’s health care challenges, Rosen’s recently-announced candidacy, and, most importantly, the perils of being a member of the president’s party in a midterm when that president is, at least at the moment, unpopular.

If Democrats can’t beat Heller, they almost certainly are going to lose net Senate seats next year, making Nevada a crucial race for both sides. In most other competitive races, it will be the Republicans playing offense, given how overextended Democrats are on next year’s Senate map.

Table 1: Crystal Ball Senate ratings change