"We're taking nothing for granted. But we are working very, very hard these last few days," Kaine told the CBS News amid reports that the Clinton campaign is scrambling in some of the traditional Democratic States like Michigan.
"We are seeing tremendous energy in registration, requests for absentee ballots, and especially early vote all across the country. What we know about the early vote in the states that have it, Wisconsin, for example, just set a record in early vote. What we see, we're really excited about," he said.
"I encouraged her to run in April of 2014. We talked about. She hadn't decided yet. But I said, no matter what the polls say and not matter what you see in an editorial, consider yourself the underdog," he said.
"You're trying to do something that has never been done. If it had been easy for a woman to be president in this country, we would have a woman president of the country. So, consider yourself the underdog until they call you the winner," Kaine said.
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"We feel very, very good about where we are, but we are taking nothing for granted. I was in Arizona earlier this week, which is a really difficult state for us, but we're making a play there. And we want to do the same here in the Midwest," he said.
Kaine said the polls started getting tighter even before the FBI letter came out in favour of reopening investigations against Clinton.
"I view that as kind of a natural tightening. At the end of a race, undecided voters, if they have a Democratic or a Republican lean, they tend to go back to their team. We are seeing that happen at the end. So, the tightening began before," he said.