Rep. Denny Rehberg (R-Mont.) will challenge Sen. Jon TesterJonathan (Jon) TesterSenate to vote next week on Freedom to Vote Act Democrats struggle to gain steam on Biden spending plan The Hill's 12:30 Report: Debt ceiling fight punted to December MORE (D-Mont.) in 2012, giving Republicans another solid candidate in a race that will be one of the party's top targets next year.  

Rehberg will officially get into the race this weekend at a GOP dinner in Montana, a Republican source with knowledge of Rehberg's plans confirmed to The Ballot Box. 

His entry into the race was first reported by Roll Call late Monday. 

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Rehberg's candidacy is more good news for Senate Republicans looking to take back the majority in the upper chamber next year. In his sixth term occupying the state's at-large congressional seat, Rehberg has a strong statewide profile and the ability to raise the funds needed for a Senate race.

It will be the second Senate race of Rehberg's career — he launched an unsuccessful challenge to Sen. Max BaucusMax Sieben BaucusBiden nominates Nicholas Burns as ambassador to China Cryptocurrency industry lobbies Washington for 'regulatory clarity' Bottom line MORE (D-Mont.) in 1996, before he was elected to the House. 

The latest campaign filings show Tester with just a modest cash edge at the start of the year. The Democrat has some $562,000 cash on hand, while Rehberg reported $553,000 on hand.

Republican businessman Steve Daines is already in the race against Tester and posted a solid fundraising start, pulling in some $225,000 since getting in. With Rehberg now in the Senate race, though, Daines is reportedly looking at a run for the state's at-large House seat instead.

-Updated at 10:05 a.m.