It is an open scandal in Washington that the Federal Election Commission is completely ossified as the referee and penalizer of abuses in national politics. Karl Rove’s powerful Crossroads GPS money machine cruelly underlined the agency’s impotence last week with a snippy rebuff of a legitimate inquiry from the commission staff about the shadowy sources of the group’s war chest. Crossroads GPS archly replied that continued inquiries on the matter “are unnecessary,” but that if they keep coming, it will offer the same unrevealing response.

This was no niggling issue. The election commission was asking for more details about the operation’s 2012 fourth-quarter report showing more than $50 million in independent expenditures but not a sign of who donated the money. The insulting rebuke to the agency should be thrown back with a unanimous demand that election law be obeyed. But this is the F.E.C., one of the sorrier federal agencies, where standoffs engineered by the three Republican commissioners on the six-seat panel have stymied efforts to write regulations and enforce them.

The result is a mounting backlog of complaints about blatant campaign abuses. Campaign operatives flout the law, knowing that the commission is toothless. The Supreme Court’s 2010 Citizens United decision deregulating campaign spending by corporations and unions has yet to be spelled out in F.E.C. rules needed by campaign operations. “Everything gets objected to,” Ellen Weintraub, a Democratic commissioner, told the journal CQ Roll Call. “Everything requires a lengthy discussion.”

At the end of this month the F.E.C., already with one unfilled vacancy, will have five members continuing to sit though their terms have expired. President Obama should fulfill his old campaign promise to nominate independent professionals to the commission. Senate Republicans would doubtlessly block his choices, but it would draw public attention to a gaping failure in a democracy that is increasingly exploited by scheming professionals.