In state after state, a gulf is opening between Republican governors willing to expand Medicaid coverage through the Affordable Care Act and Republican members of Congress convinced the law is collapsing and determined to help it fail. In recent months, insurers have increased premiums and deductibles for many policies sold online, and a dozen nonprofit insurance co-ops are shutting down, forcing consumers to seek other coverage.

But in Arizona, Arkansas, Indiana, Iowa, Michigan, New Jersey, Nevada and Ohio, Republican governors have expanded Medicaid under the health care law or defended past expansions. In South Dakota, Tennessee and Utah, Republican governors are pressing for wider Medicaid coverage. And Republican governors in a few other states, including Alabama, have indicated that they are looking anew at their options after rejecting the idea in the past.

That has created tension with Washington that some lawmakers can no longer ignore.

“I am very reluctant to take positions that counter the decisions made by the governor,” said Senator John McCain, Republican of Arizona, where more than 78,000 people have gained Medicaid coverage under legislation signed in 2013 by Jan Brewer, a Republican who was then the governor. Now, Gov. Doug Ducey, also a Republican, is seeking a federal waiver to charge premiums and co-payments and create work incentives within the limits allowed by federal rules.