This evening's face-off between the 2016 vice presidential hopefuls certainly won't have the pizzazz — or inevitable enmity — that last week's debate between Donald Trump and Hillary Clinton had.

Virginia Democratic Sen. Tim Kaine and Indiana Republican Gov. Mike Pence are two mild-mannered, affable politicians who will certainly present themselves differently than their running mates. Moderator Elaine Quijano of CBS News will try to engage them in their only debate, at Longwood University in rural Farmville, Va., but ultimately their sparring is likely to revolve as much around the principal candidates as around the vice presidential contenders themselves.

Here are four questions each man faces ahead of the 9 p.m. ET debate Tuesday:

1. Does anyone know who they are?

This is the first time the vast majority of Americans will even lay eyes on either Pence or Kaine. According to an ABC News poll, 41 percent of Americans couldn't name the GOP vice presidential candidate and 46 percent couldn't name the Democratic one.

Ultimately, that won't matter. Their job is not to debate each other — it's to score points against the presidential candidate on the other side. And although this will be the biggest audience either has ever had, the debate is not about them, or even their own readiness to be president. It's all about Clinton and Trump.

2. Will we see the opposite of the presidential debates?

This is a year when the running mates are almost completely overshadowed by the outsize personalities at the top of the ticket. Kaine and Pence don't have the sky-high negative ratings that Clinton or Trump have, and they haven't generated anything close to the interest or controversy of past vice presidential candidates (like Sarah Palin in 2008).

In fact, the two men couldn't be more different from their running mates in many ways. Pence is as smooth and disciplined as his running mate is bombastic and unpredictable. Last week he introduced himself as "kind of a B-list Republican celebrity." Meanwhile, Kaine is as amiable and as authentic (and sometimes even a little goofy) as Clinton is scripted.

Both have also broken with the past role of vice presidential candidates as "attack dogs" — willing to deliver the barbs that their running mates won't engage in. That's partly because both Kaine and Pence are even-tempered politicians with sunny dispositions. Pence even publicly rejected negative campaigning on moral grounds and promised never to engage in personal attacks — quite the opposite of Trump.

Both Clinton and Trump have shown they're more than willing to engage in the knife fights often left to the vice presidential picks. So maybe this time, just maybe, the vice presidential debates could be a little more substantive than the first presidential debate was last week.

3. How will each deal with his running mate's controversies?

Kaine has the task of trying to make Clinton seem more honest, trustworthy and likable than most voters think she is. He could also be asked to explain why she took paid speeches from Wall Street or set up her controversial private email server at the State Department.

But Kaine's task pales in comparison to Pence's burden, akin to a "clean up on aisle 7." Pence has repeatedly tried to sand down Trump's rough edges, but he hasn't always been in sync with the top of his ticket.

On climate change, for example, Pence has said he believes human activity does play a role in global warming. Trump has said that climate change is a Chinese hoax (though he falsely denied tweeting that at the debate last week). Pence could also be asked to explain why Donald Trump lost almost a billion dollars in a business deal that may have helped him avoid taxes for almost two decades, according to a New York Times report over the weekend. And he'll also surely be asked about Trump's decision to double down on comments about former Miss Universe Alicia Machado after last week's debate and to bring up former President Bill Clinton's infidelities — and to even suggest over the weekend that Hillary Clinton may not have been faithful to her husband.

Remember: Pence, who is just 57 and has long been seen as a rising GOP star, has his own political future to think about, and it will be worth watching to see how he deals with Trump's myriad self-inflicted wounds.

4. What will the VP debate accomplish?

Pence and Kaine could set the stage for the next presidential debate, which will be held this Sunday, Oct. 9, in St. Louis, by delivering new lines of attack for their principals to use. Pence could deliver Trump's anti-status quo message of change without the stream-of-consciousness distractions. Kaine could help Clinton lay out the positive message for herself that she's struggled to articulate.

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