Greg Sargent interviewed Johns Hopkins Center for Gun and Policy Research Director Daniel Webster and asked him whether background checks would reduce gun-related crimes, and also about the NRA's contention that criminals won't obey the background check laws, but will still get guns. Here's an excerpt:
Criminals won’t obey any background check laws. So why would expanding the current law do any good?
The logic of this argument is flawed. It could be used to dismiss the utility of virtually any law because criminals will disobey it. The illogical exemption of private gun sales from background checks is the very reason that criminals don’t currently have to obey existing background check laws.
State laws prohibiting high-risk groups — perpetrators of domestic violence, violent misdemeanants and the severely mentally ill — from possessing firearms have been shown to reduce violence. [1, 2] One of my studies found that a number of state laws prohibiting individuals under a domestic violence restraining order from owning guns produced an overall 19 percent reduction in intimate partner homicides. 
Meanwhile, my research has shown that state universal background checks — along with other state laws designed to increase gun seller and purchaser accountability — significantly reduce the number of guns diverted to the illegal market, where the above high risk groups often get their guns [4, 5].
At the same time, the success of these state gun laws in reducing the diversion of guns to criminals is undermined by gaps in federal laws which facilitate interstate gun trafficking from states with the weakest gun laws to those with the strongest gun laws. [6, 7] For example, we found that states without universal background check laws had 30 percent higher levels of exporting across state lines guns that were later recovered from criminals. 
There are three strong arguments for universal background checks right there. Reduction of intimate partner homicides, reduction of guns diverted to the illegal market, and reduction of guns sent to states where criminals are more likely to purchase them.
This interview is a great set of arguments for why universal background checks should be a slam-dunk. But they're not. CNN reports that the key players in the Senate negotiation are Tom Coburn and Joe Manchin.
Coburn evidently does not object to background checks but doesn't want a record of them, which is the next stupidest argument. Purchasing a car requires that it be registered, and that registration is part of a larger list of cars registered in the state. Somehow the world has continued to turn despite having to let the state know you drive a car and paying an annual fee for the privilege of doing so. So too will it turn if gun buyers have to undergo a background check and the record of that background check is maintained.
What Congress really needs to learn is how to make the NRA irrelevant to this debate. They gave up their right to influence this legislation the day Wayne LaPierre started spewing insane conspiracy theories about how the government was going to come and get their guns if they had to be even slightly accountable for them.
Chris Hayes updated the current campaign for responsible gun laws (especially background checks) on All In Wednesday night, too. Watch, because he is right on the mark: