Sen. Lamar Alexander, R-Tenn., may have breathed a sigh of relief on Tuesday when his colleague, Sen. Pat Roberts, R-Kan., defeated a tea party challenger in his primary election.
Alexander, who is seeking a third term, is the last Senate incumbent facing a serious challenge from the right during this year's primaries. All signs point to victory for Alexander, and if he wins, he will complete a sweep of primary victories for sitting senators who seem to have mastered the art of hanging onto their seats.
Alexander's challenger is state Rep. Joe Carr, who has attracted the support of a few conservative celebrities but little in the way of cash. Carr has only raised $1.4 million to Alexander's $7 million and, to make matters worse for Carr, Alexander's internal polling puts him up nearly 30 points.
"The fact that the outside money has stayed on the sidelines tells me that their polls are consistent with what in fact Sen. Alexander's campaign released last week," John Geer, a political science professor at Vanderbilt University, told CBS News earlier this week.
Geer thinks an Alexander upset in Thursday's primary is an unlikely scenario given how much he has prepared for the race and the attention he's given to the upcoming race.
He "has worked very hard over the last four years to shore up support in all quarters and he did not take anybody for granted," Geer said. "If Lamar Alexander was facing a one-on-one candidacy like a [Texas Sen.] Ted Cruz or [Kentucky Sen.] Rand Paul, someone with a lot of talent, it would be a tough battle."
But, he said, "Joe Carr is not Rand Paul. He is not Ted Cruz."
Alexander entered the race with the backing of nearly the entire Tennessee congressional delegation and Gov. Bill Haslam. Even though he has taken heat from some conservatives - especially radio host Laura Ingraham - for voting in favor of the Senate's comprehensive immigration overhaul that passed last summer it does not appear he will lose his job for it. He wouldn't be the first to survive that vote: Sen. Lindsey Graham, R-S.C., one of the immigration bill's authors, handily defeated six tea party challengers in his primary earlier this year.
The Tennessean newspaper gave a full-throated endorsement to Alexander as well, saying there is "truly no comparison" between him and Carr.
"Carr barely seems to be on [Tennessee Republicans'] radar; maybe that is because they know him too well. As a state representative, Carr is known for supporting and sponsoring the types of bills that national observers like to cite when poking fun at the Tennessee General Assembly," the editorial board wrote.
Ingraham and former Alaska Gov. Sarah Palin both endorsed Carr, but they represent the pinnacle of his outside support. Major outside grassroots Republican groups like the Senate Conservatives Fund have declined to lend their endorsements, or, more importantly, their deep pockets to his race.
But Carr hasn't given up. In a fundraising pitch last week he asked supporters to help pick up the tab for some pizza for the volunteers who came to make some last-minute phone calls Wednesday evening, according to the Tennessean.
The third viable candidate in the race is George Flinn, a Memphis radiologist and radio station owner whose own deep pockets have helped him amass a $1.8 million war chest. Both Flinn and Carr will likely win votes from the more conservative voters in Tennessee, but Geer said they would likely pick up most of their votes from their home areas of the state (Flinn in western Tennessee and Carr in the middle).