Solely because Hagel is on the ticket - Obama/Hagel.
I'm not sure on the map, Hagel wouldn't swap Nebraska and Lieberman wouldn't sway Connecticut. Both choices would be somewhat angering to the base.
Lieberman would've pissed off Republicans more than Hagel would anger Democrats. To quote
Game Change, "The base is already concerned about McCain's conservative credentials. Add to that a pro-life, Jewish VP who also happened to be Al Gore's running mate..." Obama had the base secured already. Eight years of Bush plus he energized the base by himself. Unless McCain throws out his entire career in the senate and flip flops on most issues or sprinkles some magic maverick dust its an even bigger defeat then otl.