There's a lot of gun control measures one can imagine. Within that group, there's some that are politically popular and would work. And within that group, there's a very small number of measures, or maybe none, that can pass the Republican-controlled House of Representatives, as Rep. Steve Cohen notes. But that's no reason to hold back on introducing legislation now.
If House Republicans block the legislation, or more likely, don't let the legislation come up for a vote, that's another thing you get to attack House Republicans for in the 2014 elections. And maybe when Democrats finally control the House again, we get to pass the bill. The Brady Act was introduced in 1987, and passed six years later in 1993. If someone wants to write a Newtown Bill or whatnot that would've prevented Adam Lanza from killing so many people, now is the time.