Thad Cochran in Past and present Senate candidates from Mississippi

On Principles & Values: AdWatch: American Conservative Union's lowest-scored Senator

Cochran is considered the most vulnerable Republican senator in a primary this cycle; he has faced heavy attacks from national conservative groups, which point to Cochran's votes to raise the debt limit, among others, as evidence he's not conservative enough.

He received the third- lowest score on the Club for Growth's annual scorecard, released last week, and the Club has been hitting him with ads on TV and radio. His challenger, state Sen. Chris McDaniel, has the backing of most of the prominent national conservative groups.

On Environment: The Quiet Persuader: Got $29B for Katrina rebuilding

Cochran helped obtain $29 billion for the devastated region in 2006 and earned the nickname "The Quiet Persuader" from Time magazine for steering the spending past fiscal conservatives.

He is also one of the Senate's top farm policy experts, and served as chairman of the Senate Agriculture Committee from 2003 to 2005. Cochran is playing a lead role in negotiating legislation that would reauthorize $500 billion in farm programs. He remains the top Republican on the Appropriations Committee's agriculture and defense panels.

On Government Reform: OpEd: Earmarked spending brings federal funds to Mississippi

After Cochran announced his re-election bid Friday, the Club for Growth, who have endorsed McDaniel, put out a statement that criticized the senator for his support of earmarked spending projects, for bailing out Fannie Mae and Freddie Mac and for raising the federal debt limit.

But Cochran is a formidable figure in a state that has long relied on federal largess and that rarely turns over its Senate seats. He will have the support of Mississippi's political and business establishment, which are deeply worried about what losing Cochran would mean to a state that, without him, would have little seniority in its congressional delegation.

On Principles & Values: First elected in 1978; still undecided about 2014 retirement

Cochran, 75, has not said whether he will run for a seventh term next year. He has picked up his fundraising some. Cochran, who won his seat in 1978, mingled with about 70 donors at a reception this week at the National Republican Senatorial Committee headquarters, and a source in the room said he "seemed like he was running." He suggested this summer that it might take months before he shares his plans. Asked about the attacks, Cochran's spokesman emailed: "Senator Cochran has indicated that he will determine his plans regarding the 2014 election cycle later this year."