For much of the past decade the National Rifle Association has sought to establish itself as a leading voice on judicial nominees, by condemning the candidates and then grading the votes of U.S. Senators during the confirmation process. The gun group has already served notice that it intends to wield its influence again, moving quickly this week to deride Supreme Court nominee Merrick Garland as anti-gun, based on a questionable reading of votes he took in two cases.

But a closer review of how the NRA dealt with lawmakers who defied it on the nomination of Justice Sonia Sotomayor in 2009 reveals that it is an inconsistent disciplinarian.

Nine Republicans crossed party lines to confirm Sotomayor, President Barack Obama’s first Supreme Court nominee. Five did not seek reelection, leaving Lamar Alexander, Lindsey Graham, Susan Collins, and Richard Lugar to face potential NRA retribution for their votes.

Of the four remaining, Lugar of Indiana already had a D+ rating from the NRA, for what the group perceived as anti-gun positions: most prominently his vote in the early 1990s in favor of the assault weapons ban, and his vote to reinstate the ban in 2004. In 2012, when he was up for reelection, the NRA endorsed his Republican primary challenger, Indiana state treasurer Richard Mourdock, a Tea Party favorite. The NRA ran TV ads calling for Lugar’s ouster, and a radio ad specifically mentioning his votes in favor of Obama’s Supreme Court nominees. Mourdock, who had said he would vote against Sotomayor, ultimately beat Lugar for the Republican nomination, winning 60.5 percent of the primary vote. Mourdock lost to Democrat Joe Donnelly in the general election, after he said that pregnancies resulting from rape must be in accordance with God’s plans.

The NRA downgraded Maine’s Susan Collins, a relatively moderate Republican, from a C+ to a C, and refused to endorse her during her 2014 reelection campaign. But the NRA also didn’t endorse her opponent in the primary election: long-shot write-in challenger, Erick Bennett. Collins was re-elected by a wide margin.

As fairly reliable NRA allies with solid A-ratings, Tennessee’s Lamar Alexander and South Carolina’s Lindsey Graham potentially had the most to lose when they voted to confirm Sotomayor. But the NRA endorsed both senators in their subsequent reelection battles.

Graham was considered vulnerable in that 2014 cycle, and faced State Senator Lee Bright, a conservative leader and dyed-in-the-wool gun rights advocate. But the NRA ignored Bright — and endorsed Graham in the general.

The NRA may have passed up the opportunity to punish Graham for his betrayal because of lessons learned from the Mourdock endorsement. Bright had also made controversial statements: He had talked about the possibility of South Carolina issuing its own currency as some kind of protection or protest against bank bailouts. The NRA may have realized that if it backed fringe legislators, it risked creating opportunities for Democratic opponents.

This week a few Republican Senators are testing the limits of party discipline and offering to meet with Garland. Collins, Mark Kirk of Illinois, Kelly Ayotte of New Hampshire, and Jeff Flake of Arizona have all offered to talk with Garland after the Easter recess. Kirk has an F rating from the NRA, and Collins a C rating, so they probably figure they have little to lose. But both Ayotte and Flake have A ratings to maintain.

But an A rating from the NRA can be a liability, too. Ayotte faces a close reelection fight this year. Democratic challenger Maggie Hassan has attacked her for being a tool of the NRA. Ayotte may see challenging NRA orthodoxy as a way to prove her independence.

[Photo: Tom Williams/Roll Call via Getty Images]