“I will truly miss leading and working side-by-side with these men and women in their pursuit of ATF’s unique law enforcement and regulatory mission,” Jones added. …

ATF Deputy Director Thomas E. Brandon will serve as Acting Director after Jones departs. Brandon was appointed Deputy Director of ATF in October 2011.

So far, there is no word on what prompted this sudden departure, but it’s not difficult to guess at one potential cause. The Washington Post notes the proximity of Jones’ departure to his retreat on a controversial attempt to ban ammunition for the AR-15:

Jones’s departure comes roughly one month after the ATF proposed banning armor-piercing .223-caliber bullets. The move caused an outcry among gun-rights advocates, prompting the agency to drop its plans.

Katie Pavlich’s source confirms that the negative response to Jones’ proposal broke records at the ATF:

According to one of my sources, ATF received a record breaking 300,000 comments about a February 2015 proposal to ban common AR-15 M855 “green tip” ammunition. ATF pulled the proposal after pressure from Congress and because the vast majority of comments were against the ban. The decision to pull the ban also came after ATF was caught in a “publishing mistake” in their 2014 Regulation Guidebook, which had already effectively banned the ammunition by stripping it of its “armor piercing” exemption before the public commenting period ended on March 13. The 2014 Regulation Guidebook has since been corrected and M855 “green tip” still has its exemption.

Supposedly Jones is heading to the NFL, but that wouldn’t explain the rush to get out the door. Normally, a bureau chief would give more than  11 days’ notice on exiting — even two weeks would be unseemly — which suggests that his departure wasn’t entirely his idea. If so, it will be difficult to determine whether Jones got a shove because he offered up an ignorant and likely unconstitutional ban on ammunition that has no particular danger, or whether it’s because he retreated on it. Congressional Democrats pitched a fit when Jones retreated, and it’s possible that the White House reacted similarly. Given this administration’s well-known feelings about gun ownership, the latter seems a safer bet.

Jones won’t get a second chance to revive the rule change, but we will have to see whether Obama’s next nominee wants to do so. Jones was the first ATF director to get a Senate confirmation vote, but that was when Democrats ran the upper chamber. It’ll be a much different environment for Jones’ eventual successor. Don’t be surprised if the position has another lengthy official opening.