When voters cast their ballots in January’s presidential nominating contests, they may not know the moneyed interests behind the attack ads run by shadowy outside groups trying to influence their votes, despite a Federal Election Commission deadline requiring many of them to disclose information next week. 

Although FEC regulations suggest that groups making expenditures in New Hampshire’s Jan. 10 primary must file a pre-primary report on Dec. 29, it’s not clear how many of them will do so.  

There are plenty of opportunities for these groups to avoid scrutiny until, in some cases, Jan. 31. The first ...