Four key things learned from the first debate's two nights

WASHINGTON - The first Democratic presidential debate of the 2020 election ended with a bang Thursday night, as the candidates stopped playing nice with one another and started the inevitable dirtying up of their primary campaigns.

Now that both nights are in the books, here are some combined lessons we learned.

1. Kamala Harris's singular breakout

Twenty candidates have debated, but only one seems to have made a lasting statement: Sen. Kamala Harris, D-Calif. The first night was largely nonconfrontational, but Thursday night, Harris used confrontation to her benefit. She went after the leading candidate in the polls, former Vice President Joe Biden, on an issue she knew she could speak to on a personal level: busing.

But it's one thing to pick your spots well; it's another to execute. And she did. She also bolstered her confrontation with Biden with a solid performance in other facets of the debate, including by defusing early interruptions and cross-talk by candidates who were thirsty for speaking time. "Hey, guys, you know what? America does not want to witness a food fight, they want to know how we are going to put food on their table," she said. You would have sworn it was a canned line, if it wasn't delivered in an unpredictable set of circumstances.

Whether Harris reaps a measurable benefit in polling - I'm not fully convinced she will, at this early juncture - she served notice that she is going to be a real player in this race. In case you didn't already believe that.

2. The fight for the black vote is on

Related to the point above, Biden's early support has been disproportionately built on support in the African American community. Harris's strategy both put her at the forefront and reinforced that this might be one of the most vulnerable aspects of Biden's candidacy.

I've argued for a while that Biden's lead is largely about his superior name ID and leftover goodwill from his service as Barack Obama's vice president. He was bound to come down eventually, as other candidates make themselves known. But black voters deserting him would be particularly troubling, especially if it happens on a large scale.

Harris was the only black candidate in Thursday's debate, and she did her best to test the devotion of this demographic to his campaign. It's unlikely to be the last time she, Sen. Cory Booker of New Jersey and others try to argue that they are the better option for black voters, and it will be up to Biden to make the case that touting his relationship with segregationist senators and having opposed federal busing isn't a deal-breaker.

And if Harris makes a compelling case to black voters, that could change the race faster than just about anything else, given how important they are to the Democratic nominating process. Remember that black voters were a huge and ultimately impossible-to-overcome impediment to Bernie Sanders' challenge to Hillary Clinton in 2016. They may not vote so overwhelmingly for one candidate over another in 2020, but it's a hugely important voter bloc. And now, it's being contested.

3. Sanders and Warren need to debate

One of the unfortunate realities of 20-plus legitimate candidates seeking the Democratic nomination is that they can't all face off. And that was particularly the case when it comes to Sanders and Sen. Elizabeth Warren of Massachusetts.

Sanders largely avoided the squabbles of Thursday night's debate, and nobody really went after Warren on Wednesday night. Perhaps that's because other candidates worry about alienating liberal voters who may have gravitated to either one of them - or perhaps it's because what we really need is for the two of them to make the case to what is logically a rather similar segment of supporters.

Debate is healthy. Let's hope the two get to engage in one.

4. This format has a short shelf life

Speaking of the above, the way the Democratic Party is handling these debates is less than ideal. Rather than Sanders and Warren getting a chance to debate real differences, Marianne Williamson was given the chance Thursday night to argue against emphasizing policy proposals and said her chief priority was to talk to the prime minister of New Zealand about what she would do for children.

Yes, that's perhaps reductive when it comes to Williamson's candidacy, which after all had the support of enough Democrats to qualify her for Thursday night's debate. Sorry. But at some point, the inclusion of 1 percenters such as her alongside the top candidates comes at the expense of real debate.

The DNC is making it tougher to qualify for the September debate, but they are still planning to spread the debate across two nights. Maybe Democrats allow this format for a few debates, and then adopt the GOP's 2016 approach, in which the leading candidates all got on the main stage, and the lesser candidates got a lesser chance in the "kiddie table" debate. Even aside from Warren not getting to debate Sanders, the Wednesday night debate was significantly less memorable than Thursday's, which suggests Warren pays a price for the format - and being drawn into a less-desirable field on a less-desirable night.