In an appearance on "Fox News Sunday," Kaine said McCain needs to win traditionally Republican states like Virginia.
"I do not see how Senator McCain could be president without Virginia," Kaine said.
Polls indicate Obama has a slight lead in Virginia, which has not voted for a Democratic president since 1964.
"We realize we haven't done this for a very long time in Virginia, so we're going to consider ourselves the underdogs until we finally break the string," Kaine said.
Also appearing on "Fox News Sunday," Republican campaign strategist Karl Rove said McCain has a "steep uphill climb" if he's going to win Nov. 4.
"He's got to win all of the toss-up states, 64 electoral votes, all the yellow-shaded states on the map," Rove said. "Then he needs to strip away Ohio and Indiana with 31 electoral votes to get him to 252. And then he needs to either win Colorado and Virginia, which gets him to 274, or win one of them plus Pennsylvania, which would get him to 282 or 286."