Unlike any event featuring Donald Trump, who is often incapable of controlling what come out of his mouth, Tuesday’s vice presidential debate at Longwood University in Farmville, Virginia, between Virginia Senator Tim Kaine and Indiana Governor Mike Pence—two controlled, mild-mannered politicians—promises to be a staid affair. Republican strategist Tucker Martin summed up the lack of anticipation when he told The New York Times recently, “You’re essentially following Ali-Frazier a few days later with a nationally televised book club.” Insofar as a Kaine-Pence showdown will lack the pyrotechnics of last week’s presidential debate, this is true. With the exception Joe Biden and Sarah Palin in 2008, undercard debates just aren’t as important or exciting as top-of-the-ticket debates, whether Trump is running or not.

If you’re a true political junkie, though, this is the wrong way to look at the Kaine/Pence affair. Not because the two candidates are unusual or especially compelling figures, but because in their own ways the people who selected them are. Hillary Clinton is so familiar with federal affairs that unlike most candidates, she didn’t need to select a running mate to fill some experiential need, freeing her to select someone she sees as an archetypal future leader of her party. Trump, by contrast, is so out of his depth that his running mate stands to inherit the largest political and policy portfolios in the history of the vice presidency.

Despite outward appearances, Kaine vs. Pence promises to be the most revealing and important vice presidential debate in recent history.

Part of what makes the VP debate so high-stakes this year flows straightforwardly from the reason we have vice presidents to begin with. Most of our recent presidents and presidential candidates have been relatively young, which made it actuarially unlikely their running mates would ever have to assume the duties of the presidency. The 2008 VP debate was such an unusually large draw in part because Sarah Palin was such an unexpected nominee (a kind of proto-Trump) but also because John McCain was 72 years old, and everyone recognized Palin would stand a greater-then-normal chance of assuming the presidency if their ticket won in November.

This year, both presidential nominees are older than usual. Trump is 70, Clinton is 68. For that reason alone, it makes sense to pay particular attention to who their running mates are, what they know, what they stand for, and how they comport themselves.

Going in, we know that Clinton selected a running mate who commands respect across the entire Senate, but who occupies the liberal end of the moderate wing of the Democratic caucus. Before his election in 2012, he was governor of Virginia from 2006-2010, where he was limited by law to only one term. Pence served in Congress for five terms before he became a governor, but for practically the entire time he has been a member in good standing of the GOP’s right flank.

Pence is generally well liked among Republican officials, and both he and Trump have leaned on those relationships to gain Trump acceptability within the party.

During the VP selection process, Trump’s eldest son reportedly pitched the job to potential running mates by promising that his father’s VP would be the most powerful in history, tasked with running both domestic and foreign policy, while Trump confined himself to being a spokesman for American greatness.

Pence thus embodies the reason so many movement conservatives have made their peace with Trump. They believe Trump would essentially outsource legislative negotiations to someone who, in political terms, is a more genteel version of Ted Cruz: a creature of the religious right who holds doctrinaire right-wing economic and national security views. Pence prefigured the Tea Party in opposing all the major aspects of the economic rescue in 2008 and 2009. In 2005, he supported President George W. Bush’s effort to privatize Social Security, but believed Republicans should have sought the transition to private retirement accounts more aggressively, and opposed other aspects of the Bush agenda, like the Medicare prescription drug benefit, from the right.

Many of Bernie Sanders’s supporters were unhappy that Clinton selected Kaine rather than Elizabeth Warren or another progressive to be her running mate, but Kaine fits neatly on the continuum of the Democratic Party’s slow, careful drift leftward. He has been a staunch advocate for housing and other economic rights for the poor since his days as an attorney, but he has not been the aggressive champion of welfare state and regulatory reforms. Kaine is a devout Catholic who has supported abortion restrictions in the past, but toes a pro-choice line as the Democrats’ vice presidential nominee. He fits neatly enough within the Obama tradition that in 2008 he was on Obama’s VP short list, but was passed over for being too young and lacking Capitol Hill experience.

Pence, by contrast, suggests the future of Republican Party politics will invert the pre-Trump formula, blending overt appeals to white supremacy with understated efforts to crush the New Deal. To the extent that VP’s are supposed to say something about the party and its future, Pence is the embodiment of how the GOP has tried to massage the Trump phenomenon: by running cover for him within the party and among the party’s elites while preserving the old regime in partial exile so that if Trump wins, they can jam through standard conservative movement legislation, and if he loses, they can get the old band together.

For these reasons the debate promises to be as clear a harbinger as any into America’s post-Obama political future. And because it’ll be the only debate this cycle in which both participants can speak in coherent sentences, it will be worth watching with special focus.