WASHINGTON (AP) — After two years of double-digit premium hikes, millions of people covered under the Affordable Care Act will see only modest increases next year, according to an exclusive analysis that highlights the changing politics of health care heading into the midterm elections.

The consulting firm Avalere Health and The Associated Press crunched available state data, finding that "Obamacare's" health insurance marketplaces seem to be stabilizing. Customers in some states will get price cuts. And the exodus of insurers from the program has halted, even reversed somewhat, with more cons...