Idaho U.S. Rep. Mike Simpson's bid for a ninth term got an assist Monday when former presidential candidate Mitt Romney released an endorsement letter.
Simpson faces challenger Bryan Smith in next May's Republican primary election.
Romney, the former Massachusetts governor, lauded Simpson as a "stalwart conservative leader," accusing what he called "outside" groups of interfering in the race by backing Smith.
Smith has won the conservative group Club for Growth's support in his bid to unseat Simpson.
Like Romney, Smith and Simpson come from Mormon backgrounds.
One flashpoint in this internal GOP duel has centered on which candidate likes President Obama's health care overhaul the least.
Smith accuses Simpson of not trying hard enough to repeal it, while Romney described Simpson as a lawmaker who has "fought to repeal Obamacare."