Congressional Republicans who had already vowed to oppose any candidate to fill Antonin Scalia’s seat on the U.S. Supreme Court were given additional ammunition Tuesday when President Barack Obama nominated Merrick Garland, a federal judge who played a role in two of the most important gun cases in recent decades.

Garland, 63, is chief judge on the influential U.S Court of Appeals for the D.C. Circuit, where he has served since 1997. His centrist views, and experience as a federal prosecutor with a tough-on-crime reputation, make him a relatively safe choice for the president in the face of promised Republican obstructionism in confirmation hearings. But one aspect of his record may prove especially problematic: his votes on cases involving the Second Amendment.

Garland’s most recent decision involving firearms happens to relate to the most important gun case in U.S. history. In 2007, he voted to reconsider a decision from a three-judge panel on the D.C. Circuit Court that struck down Washington, D.C.’s handgun ban. Garland wasn’t on that panel, and when the city asked for an en banc hearing, with 10 justices to reconsider the ruling, Garland voted yes. The request was ultimately rejected, on a 6-4 vote.

The next year, in District of Columbia v. Heller, the Supreme Court upheld the lower court’s decision, which invalidated the handgun ban, on a 5-4 vote. Scalia, who Garland would replace, wrote the opinion, which holds that the prohibition violates the Second Amendment’s protection of the right for private individuals to own firearms. In doing so, he handed a monumental win to gun rights advocates, who have engaged in a bitter fight for decades to overturn all gun bans, based on an interpretation of the Second Amendment as explicitly guaranteeing the right to bear arms to all citizens. (The decision did leave room for reasonable gun regulations.)

It is impossible to know how Garland may have voted had the full circuit court reviewed the case, as he indicated he thought it should. SCOTUSblog wrote that Garland’s vote for the en banc hearing may indicate that he believes the Second Amendment protects the right to bear arms solely for the purposes of service in a militia.

Garland was also a key figure in a 2000 case involving the National Rifle Association. The gun group had sued the federal government over its practice of maintaining background check records. While the the government insisted the records, which were kept for a period of six months, were used for auditing purposes, the NRA claimed they were the first steps towards a national gun registry.

Following its dismissal by a lower court, the NRA appealed the case to the D.C. Circuit Court. The court — including Garland — upheld the lower court’s ruling:

We see no basis for concluding that auditing the [National Instant Criminal Background Check System] would suddenly produce constitutional violations. Nor does the NRA identify any specific features of the auditing process that implicate constitutionally protected rights.

In light of these two cases, the National Review wrote last week that Garland’s decisions mean that he is not the political moderate that many have asserted — and that he would try to overturn Heller. The NRA tweeted the article soon after, writing: “It’s official: President Obama’s SCOTUS nomination is bad on guns.”

[Photo: AP Photo/Evan Vucci]