Three Democrats who have said they plan to break party ranks in a historic rebuke of Attorney General Eric Holder on Thursday are among the members of their party in tight races who have received the most money from the National Rifle Association's political action committee (PAC) over the course of their careers.

The National Journal reported Wednesday that Democratic Reps. Jim Matheson of Utah, John Barrow of Georgia and Nick Rahall of West Virginia have said they will vote with Republicans to find Holder in contempt of Congress because the attorney general has not released all the documents that the House Oversight and Government Reform Committee has requested on the gun-running "Fast and Furious" case. The influential and well-heeled NRA, along with a smaller but more aggressive Gun Owners of America, have signalled that they consider Thursday's vote a key one on gun rights, one that could determine which candidates will draw the groups' support — or opposition — in November.

In a letter sent to Congress last week, NRA Executive Director Chris Cox cited the attorney general's "anti Second Amendment advocacy" as a reason the organization "does not admire" him. The Gun Owners of America, a smaller but more aggressive gun-rights group, is urging readers of its website to email their members of Congress in support of the contempt resolution.

Of the Democrats in races considered competitive by political analyst Charlie Cook, the 11 who have received the most money in the careers from the NRA's PAC are among those who signed on to a letter  earlier this month asking the Obama administration to to provide "complete answers" to the House Committee on Oversight and Government Reform.  

The following chart shows the top eight recipients of NRA PAC money among the vulnerable Democrats. The two biggest beneficiaries are veteran members Rahall, who is considered likely to win by the Cook Report but not a completely safe bet, and Leonard Boswell, D-Iowa, who, thanks to redistricting, is in a difficult race with fellow incumbent Tom Latham, R-Iowa. 

The NRA, and some Republican lawmakers, have claimed that the administration was using the Fast and Furious operation to push for stricter gun control laws, an assertion that has not yet been proven in the released documents. The administration has called the manuever a political stunt. 

Still, Minority Whip Steny Hoyer, D-Md., admitted he may lose some votes to pressure from the powerful gun lobby.  

Among all of the outside groups raising funds this election cycle, the NRA PAC's haul is the 13th highest — a fact that is particularly impressive given that most of the other groups on the list are super PACs, which can raise money in unlimited amounts, and unions, which have millions of members to tap for dollars. The NRA has raised a whopping $9.2 million this cycle, and done so from a base of supporters whose donations are capped at $2,500 per election.

The vote on Holder may loom largest for Rep. Joe Donnelly, D-Ind., running for Senate in Indiana against state treasurer Richard Mourdock, a Tea Party favorite, in a race expected to be close. The NRA's PAC was heavily involved in Indiana's May Republican primary, spending over $700,000 backing Mourdock, who upset longtime Sen. Dick Lugar, R-Ind. Donnelly received the NRA's endorsement in the last election but this time may be different.

Donnelly is not the only one feeling the heat, and House Oversight and Government Reform Committee Chairman Darrell Issa, R-Calif., has predicted that at least 31 Democrats will vote with the Republicans. Among vulnerable Democrats who have received contributions from the NRA's PAC in the first five months of this year: Matheson, Rahall, Mark Critz of Pennsylvania and Ben Chandler of Kentucky.

Democrats not in competitive races who have received donations from the NRA PAC this year: Tim Holden of Pennsylvania, Tim Ryan of Ohio Kurt Schrader of Oregon and Sanford Bishop of Georgia. They were all among the 31 Democrats signing the letter asking the Obama administration to provide more information on Fast and Furious. NRA beneficiaries who did not sign the letter included: John Dingell, D-Mich., Scott Tipton, D-Colo. Henry Cuellar, D-Texas, and Brian Higgins, D-N.Y.

They won't all vote against Holder: Dingell has called the contempt vote a political stunt and will offer his own motion to refer the contempt issue back to the House Oversight Committee to conduct a more "thorough" investigation. 

So far in this election, the NRA's PAC has overwhelmingly supported Republicans–86 percent of its over $400,000 in direct campaign contributions have gone to them, with one of the biggest recipients being House Majority Leader Eric Cantor, R-Va. But also among the biggest recipients this cycle, according to the Center for Responsive Politics, are three Democrats running for reelection: Dingell, Barrow and Ryan. In the last election, the group gave nearly $1.3 million directly to candidates' campaigns, 29 percent going to Democrats, according to CRP.

But the NRA's most significant campaign influence comes from spending on ads directly supporting or opposing candidates; it doled out over $7 million on these expenditures in the 2010 election (most of it backing Republicans in seven high-profile Senate races). The NRA also spent thousands of dollars backing pro-gun rights Republicans and Democrats in the House, sometimes spending over $80,000 on ads backing some candidates. Those it supported included some Democrats who will vote against Holder, such as Rahall. Among the others it supported are conservative Democrats leaving Congress next year: Holden and Jason Altmire, who both lost primaries this year, as well as Mike Ross, D-Ark., and Dennis Cardoza, D-Calif, who are both retiring. 

(Contributing: Jacob Fenton, Kevin Koehler)