(ABC NEWS) -- As Tim Kaine prepares to walk onto the biggest political stage of his life at the vice presidential debate on Tuesday, both insiders and a former rival say one of his strongest assets will be the same thing that's helped him through a 22-year political career: His likability.

Hillary Clinton's running mate seems to know that, too. As he left mass on Sunday in Richmond, Virginia, Kaine told reporters that on Tuesday he just has to "be myself."

"I'm calm," Kaine said of his upcoming debate with GOP vice presidential nominee Mike Pence. "Things work out the way they are supposed to."

But behind the calm is intense preparation.

Long-time Democratic campaign aide Mo Elleithee has informally given Kaine thoughts and advice as he prepares for this week's debate at Longwood University in Farmville, Virginia. He worked closely with Kaine during his Senate and gubernatorial campaigns.

Elleithee said that Kaine usually begins his debate prep by working alone, reading and absorbing information, before he engages in mock debates. He said that Kaine thinks about the debate format and the best way to use that format to make his arguments.

"He doesn't have a pair of lucky debate socks or anything crazy," Elleithee said. "He takes his prep seriously, spends a lot of time thinking about how he wants to frame the arguments he wants to make."

Kaine spent the past few days prepping in both Raleigh, North Carolina, and his hometown of Richmond, Virginia. Washington, D.C.-based attorney Robert Barnett is playing Pence in Kaine's mock debates. Both members of Clinton's prep team as well as Kaine's staffers have been involved in his debate preparations.

Kaine has described this debate as a unique challenge.

"It's a different kind of a debate for me because I have done debates where it's, at the end of it, 'Please vote for Tim Kaine.' If I talk too much about Tim Kaine during my debate I'm wasting my time. It would not be a good way to use my time and it is about two visions for the country. And it's about a Clinton presidency or a [Donald] Trump presidency, so I'm more than a surrogate, because I'm on the ticket. But I am not the main event, so I'm in an in-between space. And I've not done that before," Kaine told reporters aboard his campaign plane on September 22.

Elleithee predicted that both Pence and Kaine will spend more time discussing their running mates' records than their own. Elleithee dubbed it a "proxy debate for the top of the ticket."

"These two guys can really get into a conversation about the direction each ticket wants to take the country, but there is this other layer of stuff the Clinton campaign has been trying to drive home. This notion that not only are Donald Trump's policies bad, but he's temperamentally unfit. I think Kaine is very comfortable driving both those messages and I'm sure Pence would rather focus on the former rather than the latter, but you can't escape the latter," Elleithee said.

Both Kaine and Pence will likely have to defend the vulnerabilities of the candidates at the top of the ticket, too.

For Kaine, that will likely mean defending Clinton's use of a private email server when she was secretary of state. For Pence, that may mean defending Trump's leaked tax return and his comments last week about women like Alicia Machado, the former Miss Universe whom Trump has attacked.

"Mike Pence kind of has one job in this debate and that is to change the trajectory of the race, particularly after the last week, and I'm curious to see how he does that, because the biggest problem of Trump's trajectory the last week is the perception people have of Donald Trump, and the only person who can fix that is Donald Trump," Elleithee said.

Kaine told his traveling press corps that part of his prep involved connecting Pence's record to Trump's.

"It's not knowing another fact, but it is about thinking hard about the material, thinking hard about Pence's record, and also what Pence's record would say about the guy who chose him, since it really is more about Donald Trump than it is about Governor Pence," Kaine told reporters Sept. 22.

Along with Kaine's prep, comes a sense of self that insiders say doesn’t waver even with the nerves of a big stage.

"I've never seen a debate stage Tim Kaine that looked different than Tim Kaine any other day. He is who he is," Elleithee said.

That sense of self can be frustrating for those standing on a debate stage with Kaine. Jerry Kilgore, a former attorney general in Virginia, ran against Kaine during Virginia's gubernatorial race in 2005.

Kilgore described Kaine on a debate stage coming across as "just being honest and straightforward," even when defending or explaining vulnerable parts of his record.

"He can look into that camera and absolutely be believable and unless his opponent in the debate is armed with facts he's going to get away with it," Kilgore said.

Kilgore also pointed to Kaine's background as a Harvard-trained lawyer.

"He is Harvard educated, he's an attorney and he does this sort of, he's used to like speaking to the jury and the jury in this case is the voters and he will be able to pull that off unless he's challenged," Kilgore said.

Kilgore, a Republican, has not talked to Pence, but offered this assessment.

"It will be frustrating for Governor Pence to look over and listen to Senator Kaine," Kilgore said. "He will play to the audience that is in front of him, which is the American people, trying to lure in the independent voters."

Both Kilgore and Elleithee predicted that Kaine will not engage in personal attacks on the debate stage.