Public Still Wants Background Check Loopholes Closed For Gun Buyers

We are just a couple of days away from the anniversary of the horrible massacre of twenty children and six adults in the Sandy Hook Elementary School in Newtown, Massachusetts. That shooting raised public awareness of the need for stricter gun laws in this country, especially in closing the loopholes in the background check law.
While the background check law has prevented over 2 million people (criminals and the dangerously mentally ill) from buying weapons, it cannot prevent all of them from purchasing weapons because of the huge loopholes in the law. At least 40% of gun buyers are able to skip having to go through a background check, because they purchase their guns at a gun show, over the internet, or from a private individual. That's millions of guns being sold without any regard as to who is buying them.
Congress had the opportunity to close those loopholes after the Newtown massacre. Poll after poll showed that between 80% and 90% of Americans wanted those loopholes closed. They understood that closing the loopholes wouldn't affect ordinary law-abiding Americans at all (or interfere with their Second Amendment rights), but would go a long way toward keeping guns out of the hands of those who shouldn't have them and would substantially reduce gun deaths in the U.S.
But Congress knuckled under to intimidation from the NRA and the gun manufacturers -- and did nothing. So the killing continued, at a rate of about 33 people each and every day in the United States. Personally, I think Congress must take the responsibility for a large part of those many thousands of gun deaths. Many of those deaths could have been prevented if they acted (and just done what an overwhelming majority of Americans had wanted them to do).
There are those who say the opportunity for action has now passed. That since Congress didn't act, the desire for action has subsided among the public. I don't believe that. And now there is a poll that backs me up. It is a recent YouGov Poll -- taken on December 5th and 6th of 1,000 nationwide adults (with a margin of error of 4 points). That poll showed that a huge majority of Americans (about 77%) still wants those loopholes in the background check law closed, while only 16% would oppose that.
The opportunity to act still exists, and it wouldn't even take much political courage to do it (since most people want it to happen). Why doesn't Congress act? Is it because too many of them have been bought and paid for by the NRA and the gun manufacturers?