Progressives Take Aim at Insurers in Medicare Advantage Fight

Health insurers are circulating a letter among lawmakers this month to marshal support for a program where private companies cover seniors on behalf of the government.

For the first time, that lobbying effort in favor of Medicare Advantage faces organized opposition.

For the past four years, the letter to federal officials has added new signatures—with 346 House members last Congress, or 80% of the chamber, attesting to the popularity of the plans.

This year, left-leaning organizations critical of Medicare Advantage say they’re trying to dampen support for the letter in hopes of winning better oversight and stricter rules for the ...