The Federal Election Commission, the beleaguered independent agency that is supposed to serve as the watchdog over how money is raised and spent in American elections, has long been criticized as dysfunctional, if not toothless.

Now the state of affairs at the agency is poised to get even worse: It will no longer even have enough commissioners to legally meet.

The resignation of Vice Chairman Matthew S. Petersen, announced on Monday and scheduled for the end of August, will effectively freeze the F.E.C.’s governance, leaving it one person short of a quorum and thus unable to take on some of its most basic actions, including holding board meetings, starting audits, making new rules and levying fines for campaign finance violations.

“Voters should be extremely concerned,” said Ann M. Ravel, a Democrat and former F.E.C. chairwoman who stepped down in 2017 and who has not been replaced. “If you do not have the ability to do any kind of enforcement, then there isn’t any kind of respect for the law.”