The U.S. Senate confirmed Republican lawyer Trey Trainor to the Federal Election Commission over the objections of campaign finance watchdogs, giving the agency the fourth member it needs to enforce election laws.

The Republican-led Senate confirmed Trainor on a party-line vote Tuesday. Democrats and prominent good government groups opposed Trainor’s nomination, concerned by his history of defending “dark money” groups that exploit loopholes to keep their donors secret. Campaign Legal Center President Trevor Potter, a former Republican FEC commissioner, said Trainor was being nominated to “render the agency toothless.”

Commissioner retirements and inaction from the Senate reduced the six-person commission to just three members last year, leaving the FEC without a quorum for 262 days.