Simpson is facing a tough fight against Smith, who's been endorsed by the right-wing groups Club for Growth and Madison Project. The longtime lawmaker has compiled a centrist record over the years that Smith has gone on the attack against, and conservative groups have indicated he'll be a top target this election cycle.

“Mike Simpson is so desperate to hold onto to his political career, he is now pretending to be a conservative," Smith campaign manager Carrie Brown responds. "The truth is, Mike Simpson has an across the board liberal record that includes voting for the Wall Street bank bailouts, Obama’s infamous Cash for Clunkers program, and was one of only three Republicans in the House to vote to continue to fund ACORN."

BoehnerJohn Andrew BoehnerDems face hard choice for State of the Union response Even some conservatives seem open to return to earmarks Overnight Finance: Trump, lawmakers take key step to immigration deal | Trump urges Congress to bring back earmarks | Tax law poised to create windfall for states | Trump to attend Davos | Dimon walks back bitcoin criticism MORE has already stepped up to help his friend, attending a late August fundraiser in Boise, Idaho, for Simpson.