John Richardson has the details, including this tidbit:
At the heart of this “delay” is stiff opposition from gun rights groups and their allies – including Democrats – in Congress. The Montana delegation has been particularly vociferous on the issue.
That’s because Tester and Baucus were out there in front telling people Obama wasn’t anti-gun. They have the most to lose if Obama makes them into liars. Tester is up in 2012, and Baucus in 2016. Tester, particularly, has a lot of credibility that can be flushed down the toilet if Obama decides to pick a fight with us, especially since both he and Baucus voted yes on Obama’s court picks, which we opposed.
I agree with John’s conclusion that it’s time to turn the heat up. The White House may be looking for a face saving way to say no to ATF. I would focus on the fact that they lack Congressional authority to act in this area, and are statutorily prohibited from doing what they are proposing.