In the past year, Jim DeMint, South Carolina's junior senator, has transformed himself from right-wing outlier to the Senate’s leading tribune of Tea Party sentiment. His influence has expanded despite -- or perhaps because of -- his willingness to thumb his nose at Republican Party elders, a trait that only adds to the intrigue about his ultimate intentions. Does he hope to displace Mitch McConnell, the GOP leader in the Senate? Might he harbor even loftier -- that is to say, presidential -- ambitions? Or is he content to position himself as the most conservative senator in an increasingly conservative...