The electoral consequences of passing a health care reform bill won't end with the 2018 midterms. Major provisions of the GOP's bill, including its Medicaid cuts and tax credit changes, would begin to take effect in 2020 — a year when the presidency will also be on the line and Senate Republicans will face a much tougher map than they are in 2018.
If the politics of the Affordable Care Act taught the GOP anything, it's that a major health care overhaul can significantly affect elections many cycles down the road. But on the other hand, after campaigning for years on repealing and replacing the ACA, there will be a price to pay if the party can't pass a bill.
And, even without a bill, allowing the ACA to collapse is probably politically tumultuous for the GOP as well. As one former GOP Senate staffer summed it up: "What was learned [from the ACA] is when people are angry because the system's not working for them, that's not good for anybody."