No true Libertarian or libertarian would EVER vote for an unrepentant Statist, which all Democrats are.
I'm not going to but there is one rational reason why a libertarian would vote Democrat, to tye up the government. I loved it when the republican congress and clinton were bickering all the time, even excluding the War on Terror budget needs, government spending during the 90's were lower then today.
BOTH democrats and republicans are parties of big spending. Coming from a libertarian standpoint, if they're isn't a party to reduce the size of government then we might as well tie the current one up to prevent it from getting even larger.
The two issues that prevent me from taking that standpoint are the war which needs effective leadership and judicial confirmations. I'm pro-abortion but I'll put that on the sideline to get Kelo overturned.