Democratic presidential candidate Hillary Rodham Clinton speaks in Des Moines, Iowa, on Sept. 22. (Charlie Neibergall/AP)

For the past eight years, Democrats have watched gleefully as Republicans have stumbled (and then stumbled some more) in search of both a leader and a direction.

Now it's the Democrats' turn.

The first Democratic debate of the 2016 election is Tuesday night in Las Vegas. It was long expected to be the official kickoff for the coronation of Hillary Clinton as the Democratic nominee. But as the race has developed, this debate has turned into a pinch point for a number of divergent trends within the party.

Is this a party that puts economic inequality at its core? Racial inequality? Something else or in-between? Should Democrats be open to trade deals or suspicious of them? How much power does the party establishment have? How angry are the grass roots? In the seemingly never-ending fight between labor and the environmental lobby, where does the party, ultimately, cast its lot? On foreign policy, how hawkish is too hawkish, and how dove-ish is too dove-ish?

And underlying all of those issues is this: Can the Obama electoral coalition be preserved by someone not named Barack Obama — and if so, how?

"The Democrats enter the post-Obama phase in a way that is similar to how the Republicans entered the post-Reagan era," said Dan Pfeiffer, a longtime senior adviser to Obama. "Just as the Republicans had to figure out how to keep Reagan Democrats in the fold without Reagan, the Democrats need to figure out how to keep the Obama coalition without Obama."

Of course, a two-hour debate isn't likely to answer all of these questions — or perhaps any of them. But it will begin, in earnest, a conversation about what the post-Obama Democratic party could — and should — look  like.

At the center of that conversation — and this debate — is, of course, Clinton. Clinton has staked out a series of liberal positions of late on things like the Trans-Pacific Partnership (she's opposed to it) and the Keystone XL pipeline (she's opposed to building it), but generally, seems to be cut from a similar political mold as her husband: a relentless pragmatist, not a dyed-in-the-wool liberal true-believer. That's especially true on foreign policy, where Clinton has said she supports a no-fly zone in Syria, a step opposed by, among others, Obama and Bernie Sanders.

Sanders represents a considerable contrast to the cautious and centrist policy approach typically favored by Clinton. He is unapologetically liberal about his view of the world, arguing that Democrats have, for too long, been willing to accept a half-loaf rather than pushing for the full one. Sanders also puts economic inequality at the center of virtually every issue he talks about, arguing that the gap between the rich and everybody else is the defining issue of our time and should be what Democrats talk about first, second and third.

The Sanders candidacy also represents a not-so-subtle rejection of the sort of politics that have been described for the better part of the last two decades as "Clintonian." Sanders is, in some ways, what liberals thought they were getting when they chose Obama over Clinton in 2008 — a politician who says what he believes, damn the consequences. Someone who wears the "liberal" (and even "socialist") label proudly. Someone who is willing to make people — including those in his own party — uncomfortable in trying to achieve a liberal vision of what the federal government can and should do.

Aside from pure policy disagreements, that contrast is also a stylistic and tonal one. Sanders's great strength in this race — and what has fueled much of his rise to date — is his authenticity. If you were creating the perfect candidate, you would create someone who looked and sounded like John Edwards. You would not create Sanders, a wild-haired, often-ornery, self-described democratic socialist who represents Vermont, a unique state if there ever was one. How Sanders looks and how he sounds (an incredibly strong Brooklyn accent) screams "authentic."  He is not the sort of person the Democratic Party has nominated in the recent past and, most importantly, he is not a Clinton — and all that being one represents.

Electing Clinton would likely be a return to the politics and policy that defined her husband's administration. In 2008, Democratic voters rejected that option in favor of a candidate promising a new approach — one that was defined by a more congenial and collaborative attitude toward governance. But there's no one in Washington — including Obama — who can reasonably claim that his "new" approach worked or changed anything meaningful in Washington.

So what's the right next step for Democrats? Do they return to the ways of the Clintons because of the track record of success Bill (and Hillary) Clinton built up? Or do they take another detour — this one far further off the beaten path than the one Obama represented in 2008 — to re-orient the party in the new normal of deep polarization politically, vast inequality economically and broad-scale uncertainty in foreign policy?

That conversation starts tonight. How it ends will tell us who the nominee is and what sort of Democratic Party he or she will lead.