President Joe Biden counts among his accomplishments the record-high number of people, more than 21 million, who enrolled in Obamacare plans this year. Behind the scenes, however, federal regulators are contending with a problem that affects people’s coverage: rogue brokers who have signed people up for Affordable Care Act plans, or switched them into new ones, without their permission. Fighting the problem presents tension for the administration: how to thwart the bad actors without affecting ACA sign-ups. Complaints about these unauthorized changes — which can cause affected policyholders to…