The National Rifle Association is endorsing Rep. Mike SimpsonMIchael (Mike) Keith SimpsonThe Hill's Morning Report — Sponsored by PhRMA — Tensions mount for House Republicans Koch-backed group to target some Republicans over spending vote in new ad campaign House panel votes to boost funding for Energy Dept., Army Corps MORE (R-Idaho), giving him a boost against Tea Party candidate Bryan Smith (R).

"Mike Simpson is a true conservative leader. He has led and continues to lead the way on vital firearm, hunting and self-defense reforms and issues before Congress," said NRA President David Keene in a statement before touting Simpson's "A+" rating with the group.

The NRA's endorsement could give him a big bump in the rural district — Idaho has a high rate of gun ownership, and the NRA support helps shore up Simpson's conservative bona fides.

Simpson, a close friend and ally of House Speaker John Boehner (R-Ohio), has become a top target of conservative outside groups this year. The Club for Growth and Senate Conservatives Fund are both backing Smith in the race. CFG has already spent in the race, and released a web video on Monday hitting Simpson as a "Republican in Name Only." 

Whoever wins the GOP primary will be heavily favored this fall, but former Rep. Richard Stallings (D) hopes to take advantage of the party's divisions as he makes a comeback bid for the seat he once held. Stallings, who was in Congress from 1984 until 1992 before making a losing bid for Senate, announced over the weekend.

"I have no allusions that this will be an easy campaign," he told the Twin Falls Times-News.