Hillary Clinton is talking a lot about guns. How long will that last?

There are two kinds of policy disagreements between primary candidates: the kind that involve real and significant differences and the kind where minor differences are exaggerated by one side. You could argue that the disagreement Hillary Clinton and Bernie Sanders are having over gun policy falls into the second category. Though at one time Sanders was an opponent of most gun control measures (he voted against the Brady Law, for instance), these days they actually share most of the same positions: They're both for universal background checks, a new assault weapons ban, and a number of other measures.

Nevertheless, Clinton has gone after Sanders aggressively on the gun issue, and her latest salvo is an ad that doesn't actually mention Sanders at all. If features Erica Smegielski, the daughter of Dawn Hochsprung, who was the principal of Sandy Hook Elementary in December 2012 when Adam Lanza murdered 20 children and six staff members, including Hochsprung:

There's no question that this ad is emotionally powerful. But one can't help but wonder what will happen to this issue when we're beyond the primary campaign.

The Sandy Hook massacre is particularly salient right now, not only because it remains a compelling symbol of the madness of America's gun laws and gun culture, but also because some of the victims' families are pursuing a unique lawsuit against Bushmaster, the company that made the AR-15 rifle Lanza used in his killing spree. It was somewhat surprising when the judge in the case allowed it to move forward and set a trial date, because Bushmaster and gun advocates were hoping that a 2005 law granting gun manufacturers wide immunity against lawsuits would lead to the case getting tossed out of court. Sanders voted for that law and Clinton opposed it, though Sanders recently co-sponsored a bill to repeal the law.

The lawsuit rests on the argument that because Bushmaster marketed and sold a military weapon to civilians, it knowingly created a situation where deadly violence was likely to occur, and the manufacturer should not be covered by the immunity the 2005 law granted them. The argument is something of a longshot, so there's no way to know whether it will succeed, at trial or at the inevitable appeals.

But the political calculus of the moment is clear: Clinton's position is closer to that of the Democratic electorate, so it's to her advantage to raise the gun issue. Sanders, on the other hand, is with that electorate now, but has had a much more pro-gun record in the past (that's what happens when you mount a serious run to be the nominee of a party: You move to where the center of gravity in the party is).

But if Clinton becomes the nominee, is she going to keep bringing up the gun issue? On one hand, her specific positions are widely popular. Universal background checks are supported by as many as nine in 10 Americans, and smaller majorities — but still majorities — usually favor assault weapons bans. On the other hand, there remains within the Democratic Party a widespread skittishness about bringing up the gun issue — or "taking on the gun lobby," as Clinton's ad says — and Clinton's own husband has been one of the most important voices telling Democrats not to bring up guns.

In the past, Bill Clinton has often blamed the Democrats' loss of Congress in 1994 on the gun issue, on the theory that he overrreached by passing an assault weapons ban and was punished by the National Rifle Association and American gun owners. As history, this idea is just wrong; even if you attribute every close race in that election where the NRA endorsed a candidate solely to the power of that issue, Republicans still won more than enough other races to have taken the House.

There's also a widespread myth that Al Gore lost the 2000 election because of guns. That myth says that were it not for the gun issue Gore would have prevailed in his home state of Tennessee and won the Electoral College. But there's no evidence that the issue hurt Gore in Tennessee. What mattered there was simple partisanship: The state was rapidly becoming more Republican, a trend that began before the 2000 election and continued afterward. The argument also ignores the fact that the gun issue probably helped Gore win other states.

Nevertheless, the idea of the NRA's supposedly limitless power remains, and Bill Clinton clearly believes it (unless he's changed his mind recently). And we don't yet know how much Hillary Clinton subscribes to it. It's one thing to criticize the gun lobby and make guns an issue in the Democratic primaries, where the voters are clearly on her side and it's one of the few opportunities she has to get to Bernie Sanders' left. It's something else for her to make it an issue in the general election.

And that doesn't even address what Clinton would or could do on guns as president. Given that the Obama administration has been aggressively seeking out ways to restrict the flow of guns through the use of executive actions, there may not be too many more unilateral steps Clinton could take. And the prospects for legislation on guns are always weak. If Congress couldn't pass a universal background check bill that had the support of nine out of 10 Americans (including most gun owners) right after 20 elementary school children were shot, it won't be easy to convince them to try again, to say the least.

So for a politician who's often accused of being too calculating and cautious, the gun issue offers a test. Will she only talk about it when it's to her momentary political advantage? Or does she care enough about it to keep pushing even when there's some risk involved? She might want to remember that the NRA is going to tell its members that she's coming to grab their guns no matter what she does. So if it truly matters to her, she might as well make it clear.