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.