Nine in 10 Americans, including more than eight in 10 Republicans and more than eight in 10 people from gun owning households, support expanding background checks. So why don’t Republicans fear that their opposition to a proposal that would do just that will result in a public backlash?

One key reason: Many people simply don’t know that criminals, severely mentally ill people and other high risk groups — like violent misdemeanants and people under a domestic violence restraining order — can get a gun without undergoing a check.

Joel Benenson, the lead pollster for Obama’s 2012 reelection campaign, has just published the results of a new poll — conducted by his firm for Democrats — that tells the story very well:

In a nationwide poll our firm recently conducted for the Democratic National Committee, we asked 800 voters what action they want our government to take: “enforce current gun laws more strictly but not pass new laws” or “pass new gun laws in addition to enforcing current laws more strictly.” It came as no surprise to us that they chose better enforcement by 50 percent to 43 percent. (The remainder responded “neither” or “don’t know.”)

But in the same poll, 87 percent of voters, including nearly 90 percent of gun owners, said they support background checks for all gun sales. [...]

To dig deeper into this confusion, we introduced a new series of questions. We asked this same group of voters whether or not specific laws were already on the books. Of the 50 percent of people who prefer enforcement over new laws — over half of whom are gun owners — 48 percent told us that federal laws prohibit the purchase of a weapon privately or at a gun show without a background check, while 10 percent simply admitted not knowing the rules. In other words, about 6 out of 10 people who believe we just need to do a better job of enforcing existing laws don’t realize that those laws are far weaker than they think.

This helps explain the idea behind the ubiquitous GOP talking point that we should “enforce existing laws before creating new ones.” It’s based on a gamble that many people can’t imagine that something as uncontroversial and sensible as universal background checks wouldn’t already be required.

This also helps explain why Republicans keep invoking the Second Amendment in opposing all of Obama’s gun proposals. If more voters understood that Republican officials are opposed to expanding background checks to plug a hole in existing law — even though most of those officials would probably not go so far as to say that the current background check system is a violation of Second Amendment rights — it would be much harder to ground that opposition in the Second Amendment. But since many don’t know precisely what it is Republicans are opposing, it’s easy for Republican officials to keep invoking general pieties about the Constitution.

It’s also my sense that Republicans don’t view gun violence as a motivator of voting, no matter how broad the support is for the proposed response to it (it’ll be particularly interesting to see if this holds true in some of the suburban districts House Republicans currently represent, such as those around Philadelphia). Defending the Second Amendment is a winner among Republican base voters, even if the great majority of them support expanded background checks (a dynamic that is only helped along if many of them aren’t familiar with the legal status quo).

The question is whether Dems can figure out how to extract a political price from Republicans for continued obstruction of something that literally has almost universal support. Until then, opposing everything as just another sign of of Barack Obama’s liberal gun grabbing agenda is a no-brainer for them.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.