By Amy Sullivan

Expectations for Hillary Clinton heading into the first presidential debate with Donald Trump may be unfairly high, Democratic vice presidential nominee Tim Kaine said on Thursday.

“I’m worried about that,” he told Yahoo Global News Anchor Katie Couric. “Donald’s been able to get away with some things that Hillary couldn’t, and frankly nobody could.”

“Both candidates ought to be really challenged, and challenged the same way,” said Kaine, expressing hope that debate moderators would not shy away from tough questions.

The Virginia senator cited Trump’s refusal to release his tax returns. “He’s asking us to trust him: ‘I don’t have to give you my tax returns — just trust me,’” he continued, impersonating Trump’s affect as he did during the Democratic convention. “Don’t get tricked by him.”

Kaine spoke with Couric on the campus of the University of Nevada, Reno, following a rally the Clinton-Kaine campaign held there as part of an ongoing effort to energize young voters on behalf of the Democratic ticket.

Couric, citing recent polls that show Clinton barely running ahead of Libertarian candidate Gary Johnson among millennial voters, asked Kaine what case he would make those who are considering putting their support behind Johnson and his running mate, former Massachusetts Gov. Bill Weld.

“The argument against the [third-party] ticket is, I think everybody knows they’re not going to win,” Kaine responded. “And the argument is the Al Gore-George W. Bush race in 2000. The third-party candidacy of Ralph Nader cost Gore electoral votes in New Hampshire and Florida, and if Gore had been president, we probably wouldn’t have had a war in Iraq.”

It can be tempting for dissatisfied voters to vote for an outside candidate as a way of making a statement, Kaine argued. But “casting a protest vote for a third-party candidate that’s going to lose may well affect the outcome and may well lead to a consequence that is deeply, deeply troubling,” he said. “That’s not speculation — we’ve seen it in our country’s history.”

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(Cover photo above: Renée C. Byer for Yahoo News)

Slideshow: Katie Couric interview with Tim Kaine – Behind the scenes >>>

The potential for troubling consequences is something that weighs on Kaine for personal reasons as he works to defeat Trump in November. “I’ve got a boy deployed overseas. I care so personally about who the next commander-in-chief is,” he told Couric. “I trust Hillary Clinton with my own son’s life.”

“And Donald Trump?” Couric asked.

Kaine turned to the Clinton camp’s case against Trump on national security issues. He pointed to Trump’s frequent praise of Russian President Vladimir Putin and the mogul’s openness to expanding the number of nuclear states.

“His divisive language, bromance with Vladimir Putin, thinks more nations should get nuclear weapons — Donald Trump scares me to death as a blue star family, as a military family,” said Kaine.