Carr, a Murfreesboro business consultant, told WTN-FM host Ralph Bristol that he decided to abandon his challenge to embattled U.S. Rep. Scott DesJarlais to instead take on Alexander because he considers the senator "the most liberal member of the delegation from Tennessee."
DesJarlais, a Jasper physician, is considered vulnerable because of revelations of past infidelities with patients and once having encouraged his wife and a lover to seek abortions.
In response to the switch to campaign against Alexander, Carr's top campaign strategists, Chip Saltsman, resigned.
"It is because of Lamar Alexander that people like you have the honor of serving in the majority of the state legislature," Saltsman said in his resignation letter to Carr.
Meanwhile, Alexander is one of Tennessee's most seasoned politicians. He is a former two-term governor who twice ran for president, served as U.S. secretary of education and as president of the University of Tennessee. He also had $3.1 million in the bank for his re-election effort through the first half of the year.
Carr said he expects it will take more than $5 million to defeat Alexander, including independent expenditures. He had about $275,000 on hand from his House race through the middle of the year.
"Lamar is popular, but there is a disconnect with his popularity to the way he has voted," Carr said.
In an opinion piece in The Tennessean newspaper Tuesday, Alexander defended his conservative credentials.
"I believe that one good way to put our country on the right track is to send to Washington a conservative, problem-solving former governor who worked well with others to get the results that put our state on the right track," Alexander said.
It's unclear whether Carr's entry will ward off other challengers to Alexander, who has already spent close to $1 million on his campaign, including on TV ads featuring Sen. Rand Paul, a tea party favorite, saying: "Nobody wants to say no to Lamar Alexander." Carr said he hopes to be the lone tea party candidate to challenge Alexander.
Carr was elected in 2008 to an open seat in the state House, where has sponsored legislation seeking to address illegal immigration, gun rights and reduce state sales taxes on coins and bullion. Earlier this year, he proposed making it a crime in Tennessee for federal agents to enforce any effort to ban firearms or ammunition in response to last year's shooting at a Newtown, Conn., elementary school that left 20 students and six teachers dead.
"We're tired of political antics, cheap props of using children as bait to gin up emotional attachment for an issue that quite honestly doesn't solve the problem," Carr said at the time.
The bill, which ultimately failed in a Senate committee, would have also required the state's attorney general to defend any Tennessean prosecuted for violating the potential federal gun violations.
Copyright 2013 The Associated Press.