Going into two nights of debates in Detroit, the front runners for the nomination to challenge President Trump, according to the Real Clear Politics average of presidential polls, were former Vice President Joe Biden and Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts. Five hours of intense argument and self-serving speechifying later, the contest is unchanged.

For the time being, Biden, Sanders, and Warren seem to be a class apart from the rest of the 20-plus candidates. Here's how we saw Thursday night:

1. Biden took his Geritol. He was — for the most part — focused and organized. And he didn't dodge any more questions than any other candidate. The fact that he was the object of more pot shots than anyone else is a testimony to his front runner status. (Andrew Yang deserves a gold star for asking why so much ancient history was being relitigated.) Biden may not have been as crisp as he could have been in his responses to Sens. Kamala Harris and Cory Booker when they attacked Biden for his alleged legislative racial transgressions, or to Sen. Kirsten Gillibrand when she pressed him on long-ago statements about women in the workplace. But he did not flub, and an argument can be made that they over reached.

2. Health care tops the list of issues that separate the Democratic realists from the idealists. After the last two nights, the choice for Democrats seem to be two fold: A) Medicare For all and B) Medicare for those who want it, and private insurance for those who want to keep theirs. The difference: an estimated $30 trillion. Biden subscribes to position B, and is more or less a master of its details. As for position A, no one on the stage Wednesday night was in the same league as Sanders and Warren when they defended their more radical approach Tuesday night.

3. Harris may not be ready for her closeup. The senator has lost about a third of the bump she gained last month when she bested Biden on busing. That's not all that unusual. But she didn't appear to win any of that back last night. One problem: While Harris is effective when she's on the offensive, she struggles when other candidates press her on her record and her policy proposals. Given that Harris is a career prosecutor, that comes as no surprise. Still, it should give Democratic voters searching for the most electable candidate a measure of pause.

4. Barack Obama has become an unlikely Democratic punching bag. Booker and New York City Mayor Bill de Blasio briefly had Biden on the ropes when they pressed him on Obama's aggressive deportation policy. (In the end, Biden got out of the jam by pleading loyalty-induced reticence.) As a short-term tactical move, Booker and de Blasio's attack made some sense. But it also suggests that, as a group, the Democratic candidates may not be attuned to how explosive the issue of immigration is. Obama's approach was, among other things, a de facto acknowledgment that many Americans see illegal immigration as a serious problem. If any doubt lingered, the election of Donald Trump should have dispelled it. Yet only a handful of Democrats, including Biden and Montana Gov. Steve Bullock, seem to grasp the risks the party faces here.

5. An argument could be made that with the exception of Biden, Sanders, Warren, Harris, and Mayor Pete Buttigieg, all of the other candidates would be doing the nation a service if they withdrew from the race. Yet the second debate also showed that there's genuine talent and depth in the Democratic field, from the imaginative Andrew Yang to impassioned everyman Sen. Michael Bennet to climate Cassandra Jay Inslee, the governor of Washington state. And don't forget Booker, who lurks just behind the top-tier candidates and might make a move before the race runs its course.