From The Truth About Guns:

Then, as we neared the election, the ATF dropped an October surprise, declaring some braced pistols were actually SBRs — NFA-regulated short barreled rifles — only to later back off that determination under pressure. That declaration was in direct disobedience to the Department of Justice’s edict (which happened, in a big part, thanks to Rep. Gaetz with help from brace manufacturer SB Tactical) that ATF could not pursue any new rulings or regulations on pistol braces without first setting clear standards for the accessories in cooperation with the firearm industry.