Senator John McCain recently denounced the Supreme Court’s Citizens United decision as “naïve and politically ignorant,” telling Roll Call, the Capitol Hill newspaper, that “the consequences are manifesting themselves every day in what will someday be, sooner rather than later, a huge scandal.” But Mr. McCain has no corrective, and the rest of the Republican Party seems determined to block any reform. Meanwhile, checkbook politicking has already hijacked this year’s Republican primary campaign.

The court at least offered one good antidote — that Congress mandate clear disclosure to the public of fat-cat donors now operating from campaign shadows and underwriting all of those noxious attack ads. “Disclosure permits citizens and shareholders to react to the speech of corporate entities in a proper way,” the court advised.

Democrats in Congress are pushing for disclosure, but, so far, there isn’t a Republican co-sponsor in sight. A measure from Senate Democrats would require timely disclosure by self-proclaimed independent groups that spend $10,000 or more on election ads, including the names of their major donors and a personal “I approved this ad” tag on television by the group’s chief executive. The group would have to certify that it is not “coordinating” with the candidate it obviously champions — an attempt to plug the rampant abuse of campaign law by “super PACs” and other hypocritical spenders. Democrats in the House have a similar worthy measure.

Republicans once identified with good government have an opportunity right now to reach across the aisle — before that scandal breaks. Senator McCain?