Building upon retirement rumors, Sen. Thad Cochran (R-MS) told a local paper he'll make up his mind about running for re-election within “a few weeks.” I generally believe that a sitting politician who delays announcing their re-election plans is leaning against another term.
The article also notes that Cochran is enjoying less influence in the Senate under the Democratic majority, having lost his committee chairmanship and other perks. In addition, Cochran told the paper in an interview before last year's election that his plans would be impacted by which party took control of the Senate. And we all know how that turned out.
While Cochran could probably hold his seat as long as he wants it, an open seat would present an opportunity for popular Mississippi Democrats such as former AG Mike Moore or former Governor Ronnie Musgrove.
(h/t to S2G)