WASHINGTON (AP) — The National Rifle Association has enjoyed high-profile success over the years in shaping gun-rights legislation in Congress and statehouses, in part by campaigning to defeat lawmakers who defied the group.

Now, the NRA has added a lesser-known strategy to protect its interests: opposing President Barack Obama's judicial nominees whom it sees as likely to enforce gun-control laws. In some cases, the group's opposition has kept jobs on federal benches unfilled.

Still in its early stages, the effort is a safety net to ensure that federal courthouses are stocked with judges who are friendly to gun rights, should gun restrictions somehow get through the group's first line of defense on Capitol Hill. The NRA also weighs in on state judicial elections and appointments, another fail-safe if the massacre of young children at a Newtown, Conn., elementary school leads to tighter gun-control measures.

A case study in the group's approach across the country can be found in its opposition to the nominations of the two most recent Supreme Court justices.

The NRA opposed both Sonia Sotomayor and Elena Kagan and warned its allies in Congress that their votes to confirm each would be held against them.

In a letter to lawmakers, the NRA wrote: "In testimony before the Senate Judiciary Committee, (Kagan) refused to declare support for the Second Amendment, saying only that the matter was 'settled law.' This was eerily similar to the scripted testimony of Justice Sonia Sotomayor last year, prior to her confirmation to the court. It has become obvious that 'settled law' is the scripted code of an anti-gun nominee's confirmation effort."

It added, "The NRA is not fooled."

The group had limited evidence to back up its claims that the two were opposed to gun rights. It pointed to a one-paragraph memo Kagan wrote in 1987 to Justice Thurgood Marshall that suggested she was not sympathetic to gun owners, and to her time as a lawyer in the Clinton administration as it sought to put tighter gun controls in place. For Sotomayor, critics cited a ruling that upheld New York's ban on nunchucks, a martial arts weapon that has nothing to do with firearms.

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Even some pro-gun-rights lawmakers bristled at the NRA inserting itself into judicial confirmation battles.

"I am a bit concerned that the NRA weighed in and said they were going to score this. I don't think that was appropriate," Republican Sen. Lisa Murkowski of Alaska said at the time. "A vote on a Supreme Court justice, in my mind, should be free from those political interest groups that are going to pressure you."

But, like most Republicans, she still voted against confirming both nominees, likely for reasons beyond the gun issue.

Only seven GOP senators voted for Sotomayor in 2009 and, a year later, only five Republicans voted for Kagan.

Among those who supported both was Sen. Richard Lugar, a six-term Indiana Republican who lost his seat last year in a primary.

The NRA exacted its revenge in that race, spending $200,000 against him in order to help GOP challenger Richard Mourdock.

"Dick Lugar has changed. He's become the only Republican candidate in Indiana with an F rating from the NRA," the group said in one TV ad. The group also warned allies that Lugar voted to confirm "both of Barack Obama's anti-gun nominees to the U.S. Supreme Court."

Last spring, the group opposed the nomination of Elissa Cadish to the federal bench in Nevada and worked with Sen. Dean Heller of Nevada to block it.

In 2008, while running for a district court position in Nevada, Cadish replied on an election-year survey that "I do not believe that there is this constitutional right" to guns. She added, however, "Of course, I will enforce the laws as they exist as a judge."

Cadish completed the Citizens for Responsible Government questionnaire before the Supreme Court ruled in 2008 that the Second Amendment protected a citizen's right to have firearms in the District of Columbia and before a 2010 case that gave the same rights to citizens who live in the states.

Four years later, when Obama nominated her to a federal bench, she faced questions about those views and sought to clarify her position in a letter to her state's other senator, Harry Reid.

"I want to assure you that I was not giving my personal opinion on this question," Cadish said. "Rather, this response was based on my understanding of the state of federal law at the time."

The NRA questioned the sincerity of Cadish's statement.

"While she has more recently tried to backtrack from that statement, her 'new' position is of little comfort to gun owners," NRA executive director Chris Cox wrote to Heller in April.

In the months that followed, the NRA and its affiliated groups spent $98,467 to help Heller win election, including a television ad promising Heller would "oppose any anti-gun nominee to the Supreme Court."

"This election's not about the next four years. It's about the next 40 years. So vote like your freedom depends on it. Because it does," Cox told audiences in that ad.

Similarly, the NRA has helped block Caitlin Halligan's rise from the Manhattan district attorney's office to the U.S. Court of Appeals for the District of Columbia Circuit, a launching pad for several Supreme Court justices. The group pointed to her work on New York's 2001 lawsuit against gun makers and opposition to a 2005 federal law that shielded firearm companies from liability for crimes committed with their wares.

"Given Ms. Halligan's clear opposition to a major federal law that was essential to protecting law-abiding Americans' right to keep and bear arms, as well as an important industry that equips our military and law enforcement personnel, we must respectfully oppose her confirmation," Cox wrote the lawmakers in 2011.

That appeals court seat has remained vacant since 2005, when President George W. Bush nominated and the Senate confirmed John Roberts as chief justice on the Supreme Court.

Last Thursday, Obama renominated both Cadish and Halligan and urged the Senate to vote.

"I am renominating 33 highly qualified candidates for the federal bench, including many who could have and should have been confirmed before the Senate adjourned," Obama said.

Yet there was no signal the NRA would drop its opposition.

The group's deep pockets help bolster allies and punish lawmakers who buck them, on judges or legislation. The group spent at least $24 million in the 2012 elections — $16.8 million through its political action committee and nearly $7.5 million through its affiliated Institute for Legislative Action. Separately, the NRA spent some $4.4 million through July 1 to lobby Congress.

In one case, the group spent about $100,000 — a tremendous sum for a state legislative race — to mount a primary challenge against a Republican Tennessee lawmaker, Debra Maggart, because she wouldn't toe the NRA's line in Nashville.

As the NRA works to put its stamp on another branch of government, its influence could be even more lasting — federal judges are appointed for life and aren't subject to voters in election years.

EDITOR'S NOTE _ An occasional look at how special interests exercise behind-the-scenes influence.