A new ad blasts President Obama and Senate Majority Leader Harry Reid, accusing them of "pulling the strings" to get Montana Lt. Gov. John Walsh appointed as a senator to give him a leg up in the 2014 election.

Walsh was already a Democratic candidate to replace Sen. Max Baucus, D-Mont., who had planned to retire. But Obama nominated Baucus as ambassador to China, and the Senate confirmed his nomination on Thursday.

Democratic Gov. Steve Bullock said Friday he would appoint Walsh to the seat, prompting the National Republican Senatorial Committee to release an ad blasting the move as part of a corrupt bargain.

Walsh, who's expected to be sworn in Tuesday, now has an advantage, since he will face voters as an incumbent while serving the remainder of Baucus' term. He still faces an tough election, however, as early polls show him trailing Republican Senate candidate Rep. Steve Daines by as many as 14 points.