Winning isn’t everything, but losing just might be. In fact, coming in second has been a career booster for some high-profile losers who by rights should be on the trash heap of also-ran-dom. Take ”American Idol”’s Clay Aiken. Not only did the angel-faced crooner’s second-place performance land him on the cover of ”Rolling Stone” before AI winner Ruben Studdard, but his debut CD, ”Measure of a Man,” sold a commanding 613,000 copies in its first week of release (Studdard’s hits Dec. 9). ”I almost feel like the fact that he ended up being a runner-up kind of added to his appeal,” notes ”Billboard”’s Geoff Mayfield. No doubt that idea is what prompted the folks behind ”The Bachelor” to cast unlucky-in-made-for-TV-love runner-up Trista Rehn. Then there’s ”Bachelorette” reject Bob Guiney, perhaps the most lovable (turned kiss-happy) loser making hay on the small screen. Hey, in a country where not actually winning the popular vote can lead to the Oval Office, it pays to aim low.