Washington (CNN) -- When the National Rifle Association decided to keep track of those House members on both sides of the aisle who voted to hold Attorney General Eric Holder in contempt of Congress last week, it was also sending a message to a number of embattled Democratic congressmen seeking re-election in conservative districts in the fall.
The message: Vote right, or we'll let your constituents know.
Though some Democrats say the NRA did little to influence their vote, for a handful of those in the House, the message may have been received loud and clear, experts say.
A CNN analysis showed that of the 21 Democrats who voted to hold Holder in civil contempt of Congress last week over documents relating to Operation Fast and Furious, 19 received campaign contributions from the NRA during the last two election cycles.
During that period, all of the 21 were targeted by the National Republican Campaign Committee, signaling the organization's desire to turn the competitive districts from blue to red.
And of the 17 Democrats who voted in favor of criminal contempt Thursday, all received campaign contributions from the NRA during the same time and have faced similar Republican campaign committee threats.
One Democrat who voted for the contempt charges said he did so on principle, not politics.
"The attorney general was asked to provide information, and he chose not to provide. So as a result, I had no other choice but to vote in contempt," Democrat and Pennsylvania Rep. Jason Altmire told CNN's Soledad O'Brien.
Still, in this year's ultracompetitive seats -- particularly those that have been subject to redistricting -- a nod from the NRA for a Democrat could make the difference between re-election and retirement.
The NRA raised the stakes of the vote for members in competitive districts when the organization announced that it would score the vote -- or publicly count any vote against holding Holder in contempt as a mark against a lawmaker seeking re-election.
Out of those seeking re-election who voted in favor of contempt, more than half are listed in competitive districts by the Cook Political Report and rely on conservative support, including endorsements from the NRA, to survive their tough political battles.
Efforts to seek comment from the NRA were not successful.
Of the 26 Democrat members in the House who received money from the NRA in 2012, the 12 who abstained or voted against contempt do not have notably competitive races, a CNN analysis found.
"(The contempt vote) is a fairly low-cost way to demonstrate independence from your own party. The vote was going to pass anyway, so why not take the opportunity to say you can buck your own party," said Dave Wasserman, House race editor at the Cook Report.
"Democrats in those types of districts love to have an NRA endorsement because it bolsters their standing with a demographic they need to cut into to survive," Wasserman said.
Among them is Rep. John Barrow, D-Georgia, who is facing perhaps the toughest re-election campaign out of the 435 House seats up for election come November.
Barrow, one of the few white Southern Democrats left, found himself in a more conservative district after the Georgia General Assembly completed a controversial congressional redistricting process last year that left 12 Democratic seats more uncertain than they were last election.
In addition to the NRA's influential endorsement listed on his website, Barrow received $9,900 in 2010 and $4,000 this year in PAC-to-PAC contributions from the gun rights organization.
The 26 Democrats to whom the organization contributed during the 2012 election cycle have received an average of about $2,100, totaling $54,450, according figures collected by the Center for Responsive Politics.
Barrow declined a request for comment but released a statement before the vote depoliticizing his support.
"For me, this investigation has been about justice for Border Patrol Agent Brian Terry and his family," Barrow said. "The only way to get to the bottom of what happened is for the Department of Justice to turn over the remaining documents, so that we can work together to ensure this tragedy never happens again."
There is no doubt that Barrow is a Republican target.
"It's pretty clear ... that these Democrats are going to do everything they can between now and November to distance themselves from the administration and the unpopular agenda," National Republican Campaign Committee Press Secretary Paul Lindsay said.
Democratic leaders, meanwhile, aren't standing still.
The DCCC launched Monday a campaign of its own to target House Republicans in key races this fall, highlighting their votes against health care reform. They will unleash a torrent of live and robo-calls, hitting 10 GOP House races where they perceive vulnerability — including Rep. Dan Lungren and Rep. Mary Bono Mack of California, Rep. Judy Biggert of Illinois and Rep. Chris Gibson of New York. And all 10 voted to hold Holder in contempt.
For four-term congressman Altmire, he said he was being consistent in his vote against Holder, using the same strategy he touted during the 2010 election and in campaign ads.
"Too many people in Congress just tote the party line. Jason Altmire isn't like that." his ad said. "No doubt about it. You saw he voted against health care. Jason opposed the Wall Street bailout. I think Jason is not afraid to stand up to the president. And Nancy Pelosi. He fights for folks here," the ad continued.
Altmire, who lost a primary battle to colleague Rep. Mark Critz after redistricting landed the pair in the same district, told O'Brien that he voted in favor of contempt because it was consistent with his vote to hold Bush administration White House Counsel Harriet Miers in contempt in 2008. Miers refused to show up for a congressional subpoena or to hand over documents relating to the firing of a large number of U.S. attorneys.
"I don't like to play those kind of political games. I stayed consistent with the vote I cast in 2008."
Approximately half of the Democrats who voted in favor of contempt also voted against health care reform, including Barrow; Rep. Ben Chandler, D-Kentucky; Rep. Larry Kissell, D-North Carolina; Rep. Jim Matheson, D-Utah; Rep. Mike McIntyre, D-North Carolina; Rep. Collin Peterson, D-Minnesota; and Rep. Mike Ross, D-Arkansas.
"In some cases, it's a heartfelt vote, but in most cases, it's political survival," Wasserman said of the votes embattled lawmakers make across the aisle.