Vice Presidential Candidates Prep for Their Debate

They face off on Tuesday in Virginia.

— -- Donald Trump may have boasted about shunning traditional debate prep, but his running mate and Hillary Clinton's aren't leaving anything up to chance.

Before Gov. Mike Pence, R-Indiana, and Sen. Tim Kaine, D-Virginia, face off at Longwood University on Tuesday, they're both working on their debate skills this week.

Unlike their running mates, the topics for the vice-presidential debate will not be announced by the Commission on Presidential Debates beforehand, meaning that Pence and Kaine have to be ready for anything.

While in Madison, Wisconsin, on Tuesday, Pence teased that he was getting some help from Gov. Scott Walker.

Pence told supporters he was in town doing "doing a little bit of debate prep of my own with a very good man who is putting me through my paces."

That work was confirmed by Walker on Twitter on Thursday.

ABC News has been told that Walker is formally acting as Kaine's stand-in during debate preparations.

Kaine was off the trail entirely on Thursday, spending the day in Raleigh, North Carolina, to do his debate prep. Earlier this week, he studied during a plane ride from Orlando to Washington, D.C., while his guests tried to be respectful.

During the Monday flight, Sen. Bill Nelson, D-Florida, spoke to the press corps and said that he was keeping quiet so Kaine could focus. But Nelson did offer some advice for Kaine, saying he needs to “be himself."

"He is a good person to his core," he said. "And deep down, that’s what a lot of voters look to ... is this a good person. And I think he will exude that because he is what he is.”

ABC News' Jessica Hopper and Ines De La Cuetara contributed to this report.