The 52 Republican senators have been meeting several times a week behind closed doors to develop a bill to repeal and replace the Affordable Care Act. At least 50 of them must be on board for the bill to pass.

Republican senators are arranged based on their ideology scores

13 of them, highlighted below, are leading the effort. They are members of a working group created by Mitch McConnell of Kentucky, the majority leader. The group includes two of the most conservative senators – Ted Cruz of Texas and Mike Lee of Utah — but excludes several prominent moderates.

Mr. McConnell faces the same challenge that Speaker Paul D. Ryan confronted in the House. A bill that caters to conservatives risks alienating moderates.

Most senators want to make sure that people with pre-existing conditions are protected, but over all, they have different priorities. The fate of the health care bill could ultimately be decided by a handful of senators.

Mr. Cruz and Mr. Lee would rather have a full repeal of the Affordable Care Act. Rand Paul of Kentucky has said that he doesn’t think the House bill passed in May went far enough. He said he did not want to replace the Affordable Care Act with “Obamacare Lite.”

Senator Pat Toomey of Pennsylvania wants to overhaul Medicaid and would go…