No doubt, there’s never as much portent in a running mate debate as when the two presidential nominees square off, and the rhetorical fireworks won’t come close to what we’ve already seen from the ticket toppers.

But this time looks to be special for other reasons, mainly having to do with genuine substance, which is why undecided voters and Beltway insiders have good reason to devote 90 minutes to watching television Tuesday night.

On experience and affect, the contrasts between Tim Kaine and Mike Pence are much more subtle than the Baroque differences between Hillary Clinton and Donald Trump.

But on partisan ideology and tangible policy records, the vice presidential candidates are much easier to tell apart these days than the national standard bearers. Their voting records in Congress during Barack Obama’s presidency leave no doubt about that.

Both nominees for No. 2 have deep and diverse experience in government and project a studied thoughtfulness. That may come off as boring. But it should nonetheless inspire confidence that, if tragedy occurs, either would accept the world’s most important field promotion with the right combination of confidence and humility.    

Both also have more than two decades of practice at campaign debates, Pence’s beginning with a series of congressional races starting in 1988 and Kaine’s during a steady rise from the Richmond city council in 1994 through lieutenant governor and then governor.

Pence won Indiana’s governorship after three debates in the fall of 2012, when Kaine debated five times in Virginia before securing his Senate seat. Reviewing footage of those encounters makes clear that both men are clearly adept at selling their agendas — and at condensing complex policy matters into shorthand that’s both factually solid and understandable to the typical voter.

Finally, both are adept at seizing openings left by their opponent and unafraid to mix it up with the person standing at the other podium — although Pence maintains an intensely cool tone in such confrontations while Kaine allows himself to appear like he’s getting just a little worked up.

What will make things different at Longwood University in Farmville, Va., is that neither Kaine nor Pence are trying to get elected in their own right. Instead, their performance objectives are only to counterbalance the perceived shortcomings, and underscore the strengths, of their running mates.

Pence has the much tougher assignment. And that’s not only because it will require a projection of almost superhuman calm and level-headedness to quell anxieties that many voters have about Trump’s hyperbolic and undisciplined persona.

Pence is also trying to navigate an ideological balancing act. He’s expected to reassure conservative Republicans that a Trump administration would approach governance from the right. But he’s also hoping to give the undecideds, and those drawn to Trump’s outsider status, reason to believe his presidency would be about breaking the bonds of reflexive partisanship.

On that front, Pence pointing to his own voting record would be of minimal help.

During his final two terms in the House, which coincided with Obama’s first term as president, no Republican toed the party line more loyally during roll calls during which most in his caucus voted one way and most Democrats did the opposite — a 99 percent party unity score. On 1,955 such votes, Pence went against the grain just 24 times.

And only two-dozen Republicans who were in the House during all four years voted less frequently the way Obama wanted — just 50 times, or 20 percent of the occasions when the president’s wishes were clearly expressed in advance, according to CQ Roll Call’s Vote Watch database.

Kaine’s presidential support and party unity records stand in dramatic contrast. And they afford him solid evidence for his contention that he’d be at once a loyal Clinton lieutenant and a seeker of the legislative middle ground.

Since joining the Senate, Kaine has voted against Obama’s wishes a scant five times — a 98.6 percent presidential support score that no current senator has exceeded. (Two have backed Obama as often, during his second term, fellow Democrats Chris Coons of Delaware and Bill Nelson of Florida.)

During that same time, however, Kaine has somehow managed to construct one of the more bipartisan, or at least more iconoclastic, senatorial voting records. He’s gone against the Democratic mainstream in four-dozen ballots that split mostly on partisan lines — a 94 percent party unity score during the last four years that’s lower than all but seven of his current Democratic colleagues.

Even if these numbers aren’t mentioned Tuesday night, they still provide insight about how Pence or Kaine might behave during the next big step up in their careers.

And that behavior could well draw more attention than is usually paid to the vice president. Five weeks from Election Day, there are several viable pathways to the creation of a 50-50 Senate for next year, which would mean plenty of potential use for the vice president’s tie-breaking powers.

And history says that, whichever running mate gets elected, he’ll have a one in three chance of having the top job someday. Fourteen of our 44 presidents were previously vice president.