A thought-provoking post by Sean Trende:

Even worse for Republicans, consider some of the candidates who lost pretty close races in ’02 or ’03: Matt Salmon in Arizona, Bill Simon in California, Jim Ryan in Illinois, Bobby Jindal in Louisiana, Dick Posthumus in Michigan, Steve Largent in Oklahoma and Scott McCallum in Wisconsin. I tend to believe that had they won in 2002, been re-elected in 2006 (and avoided scandal), most of these candidates would be in the presidential mix right now.

Every election counts, it seems.