(CNN) — Tim Kaine and Mike Pence were on the debate stage Tuesday but their clash really centered on two other people: Hillary Clinton and Donald Trump.
Kaine, Hillary Clinton's running mate, said that for him and his wife, who have a son deployed overseas as a Marine, "the thought of Donald Trump as commander-in-chief scares us to death."
He hammered Trump over his temperament, accused him of pursuing an "outrageous lie" over claims President Barack Obama was not born in the United States and condemned him for calling Mexicans criminals and rapists in his announcement speech last year.
Pence didn't hesitate to defend the controversial candidate at the top of the GOP ticket. He defended Trump by trying to turn the focus back on Clinton, accusing her family's foundation of accepting donations from foreign governments while she was secretary of state and slamming her over the private email server she used while in office. Pence argued that Kaine was a fitting running mate for Clinton because he had tried, but failed, to raise taxes while serving as Virginia Governor.
"Hillary Clinton and Tim Kaine want to build on Obamacare," Pence said. "For all the world, Hillary Clinton just thinks Obamacare is a good start."
Pence also defended Trump over a story in The New York Times that revealed he declared a $916 million loss in 1995 and may have therefore been able to avoid paying income tax for 18 years. He said that Trump, unlike Clinton and Kaine, was not a career politician.
"He actually built a business. Those tax returns showed he faced some pretty tough times 20 years ago," Pence said, adding that the tax code was designed to allow businessmen like Trump to comeback after taking risks.
Sudden political significance
The rival running mates repeatedly interrupted each other -- and debate moderator Elaine Quijano of CBS -- during the debate. They lack the charisma and notoriety of their celebrity superiors on the Republican and Democratic tickets, but their clash at Longwood University in Farmville, Virginia, is taking on sudden political significance at the end of a turbulent week in which Trump veered off message and took a beating in the polls.
Pence faces a daunting high-pressure assignment of stopping the bleeding in Trump's campaign after the GOP nominee has repeatedly failed to do himself over the past week. For Kaine, the showdown offers a precious prime-time chance to skewer Trump over a string of controversies unleashed by the GOP nominee's poor debate showing last week. The Virginia senator can also road test fresh attacks that Clinton can use in the second presidential debate on Sunday, which will be moderated by CNN's Anderson Cooper.
Both men, vying to be a heartbeat away from the presidency, are aiming to introduce themselves to viewers mostly unaware of their own successful, yet under-the-radar political careers.
Pence has a chance to lay out the kind of prosecution of Clinton's liabilities -- including some aspects of her record as secretary of state, her private email server and status as a pseudo incumbent faced with an electorate that wants change -- that Trump failed to pull off at his own debate last week.
The Trump campaign badly needs him to succeed.
The GOP nominee's own disappointing debate performance, and erratic off message behavior since, could be turning the race for the White House against him. Clinton has now pulled out a clear lead in most national polls released after the debate, reversing Trump's momentum. And the former secretary of state has also restored a strong position in swing state polls, just five weeks before election day.
Kaine probably has the easier task ahead of him on Tuesday night.
He is certain to try to force Pence on the defensive over reports that Trump may not have paid income tax for 18 years after declaring a $916 million business loss in 1995, revealed in a blockbuster New York Times story.
He will also likely try to frustrate Pence's efforts to move the campaign to sounder political ground by raising Trump's tirades over against former Miss Universe Alicia Machado, who says she was insulted by the GOP nominee during his time as a beauty pageant impresario.
Kaine may also try to probe the sharp differences on political philosophy between Pence and Trump -- on issues ranging from trade to Trump's birtherism crusade to foreign policy -- that make the Indiana's governor's position on the GOP ticket a balancing act.
The current vice president, Joe Biden, offered some pointers to Kaine in an interview with CNN's "New Day" on Tuesday.
"I don't know that he really thinks a lot of what Trump is saying makes any sense," Biden said.
"What a hell of a way to make a living, to be vice president and have to get up every morning and support someone you don't agree with," Biden continued. "Maybe he does. And if he does agree with him, then people can see the difference in policy here."
Biden on Trump: 'He's not a bad man, but his ignorance is so profound'
Still, a strong performance by Pence could allay concerns that the Clinton campaign has been playing up about whether Trump has the temperament and knowledge to serve as commander-in-chief.
Both Pence and Kaine have been preparing carefully for the debate.
The Virginia senator will be on home turf on Tuesday night and has been huddling with top members of the campaign team who prepared Clinton for her debate with Trump last week, including Democratic debate gurus Ron Klain and Karen Dunn. Kaine has consumed background material and gamed out approaches to lay out the stark difference between the two tickets, a campaign adviser said.
Unlike Trump, who disappointed aides with his debate prep, Pence has been getting ready for the debate ever since he was picked for the Republican ticket in July. He's been helped by Wisconsin Gov. Scott Walker and an aide said he was "more than ready" to answer attacks on the GOP nominee over his taxes.
Pence, a well regarded figure among the Republican Party's most conservative constituencies, could help Trump by reassuring traditional GOP voters that they will have an ally and an advocate in the White House. The Republicans would rather the debate turn on a contrast between Pence and Kaine rather than Clinton and Trump.
"When Tim Kaine was governor, taxes went up, unemployment went up. When Mike Pence was governor in Indiana, taxes have gone down. I think you're going to see a huge contrast in their records and a huge contrast in the tone," Republican National Committee Chairman Sean Spicer told CNN's "New Day."
Kaine, meanwhile, could help bolster Clinton's lead in his own state of Virginia and appeal to African-American and Hispanic communities that could be crucial in some battleground states. Both he and Pence, a former congressman, are well-versed in foreign policy, should the debate turn that way.
In terms of style, Kaine and Pence both provide sharp contrasts with their superiors on the ticket, both of whom are controversial, outspoken and polarizing figures who have lived in fame's glaring spotlight for decades.
Civil, courteous candidates
Both are known as civil, courteous men despite their strong political beliefs. They are also devoutly religious. Kaine is a practicing Roman Catholic and Pence a Catholic who is now an evangelical Christian. Pence used to say in his days as a conservative talk radio host in courtly Indiana that he was like a decaf version of Rush Limbaugh.
So if there is ever going be a substantive, in-depth debate about the differences between the policies Clinton and Trump are advocating, the vice presidential debate may be the mostly likely venue for it to occur.
Typically, vice presidential debates lack the huge stakes, massive television audiences and capacity to shape races seen in debates between the two party nominees.
But they are sometimes significant. In 2012, for example Biden steadied a nervous Obama re-election campaign with a strong performance in the vice presidential debate that set the tone for the President's own comeback following a poor first debate showdown against Mitt Romney.
And in 2008, Republican vice presidential nominee Sarah Palin staved off a widely predicted disaster and did just enough to remain a credible vice presidential pick --- though the campaign was later overtaken by the financial crisis.
A new CNN/ORC poll Tuesday showed that Pence and Kaine are equally matched.
A equal block of 38% of voters expect each man to do the best job. Both candidates have positive net favorability ratings but almost 3 in 10 of voters have no opinion of either man.