On Capitol Hill, there’s literally only one member of Congress who describes himself as a European socialist. I’m referring, of course, to Sen. Bernie Sanders (I-Vt.), who launched his Democratic presidential campaign last week, to the delight of many progressive activists.

And why not? Sanders isn’t favored to actually win the Democratic nomination, but the Vermont senator has a bold, progressive vision, and is prepared to take advantage of the national platform a White House campaign offers. For liberal voters who yearn for a standard bearer whom no one has ever considered a “moderate,” Sanders is a welcome breath of unapologetic fresh air.

There is, however, an exception to Sanders’ liberalism. Mark Joseph Stern highlighted it at Slate this week.

[ B]efore liberal Democrats flock to Sanders, they should remember that the Vermont senator stands firmly to Clinton’s right on one issue of overwhelming importance to the Democratic base: gun control. During his time in Congress, Sanders opposed several moderate gun control bills. He also supported the most odious NRA–backed law in recent memory – one that may block Sandy Hook families from winning a lawsuit against the manufacturer of the gun used to massacre their children. Sanders, an economic populist and middle-class pugilist, doesn’t talk much about guns on the campaign trail. But his voting record paints the picture of a legislator who is both skeptical of gun control and invested in the interests of gun owners – and manufacturers. In 1993, voted against the Brady Act , which mandated federal background checks for gun purchasers and restricted felons’ access to firearms. As a senator, Sanders supported bills to allow firearms in checked bags on Amtrak trains and block funding to any foreign aid organization that registered or taxed Americans guns.

In fairness to Sanders, the senator does not always see eye to eye with the far-right gun group, but over the course of his congressional career, the Vermont independent has generally sided with the NRA on most of the major legislative fights regarding gun policy.

Indeed, it’s probably safe to say that Sanders will be to Clinton’s left on most issues in their primary fight, except when it comes to guns.

To understand why, it’s important to realize that Vermont has some of the most lax gun laws in the nation, in large part because gun violence in the Green Mountain State is so low.

Indeed, a wide variety of prominent Vermont Democrats and liberal independents routinely enjoy support from the NRA. Former Gov. Howard Dean, his reputation as a liberal firebrand notwithstanding, was endorsed by the NRA in Vermont more than once – a fact he used to brag about during his 2004 presidential campaign.

It’s easy to forget, but back in November 2003, when it looked like Dean was surging in the race for the Democratic nomination, John Kerry actually used this against the Vermont governor: “We don’t need to be a party that says we need to be the candidacy of the NRA. We stand up against that.”

With this in mind, Sanders is simply in line with his home state’s political norms. His position may not be expected given his reputation in D.C., but in Vermont, it’d be odd if Sanders didn’t oppose many gun reforms.

It’s tough to say whether progressive activists who’ve rallied to the senator are going to care much about this, and it’s a safe bet that Sanders won’t make opposition to gun-safety measures an important part of his 2016 pitch. But as the campaign progresses, it’s an angle worth watching anyway.