There was something different about the Democratic debate this week, compared to the earlier rounds this summer. Something was happening that was hard to pin down, but palpable. Not the contrast of night and day, but perhaps the difference between dusk and dawn.

It’s a critical difference and it comes at a crucial time. Because the Trump presidency these candidates are competing to truncate has reached what may be a critical juncture. But more of that in a moment.

This week, the Democratic nomination fight once again took the form of a TV quiz show with too many contestants to fit onscreen at once. Once again, the candidates sounded a lot alike, peddling much the same wares as in June and July. And yes, three hours was too long.

Yet something different happened. The debate left a clearer imprint. The effect was at least somewhat more energizing than the summer meetings, or perhaps just a bit less dispiriting.

There were still 10 candidates on stage but at least they were the candidates most people wanted to see and — best of all — there was not the prospect of 10 more contestants doing it all over on the following night.

That made a difference. The earlier affairs had the feel of the NFL exhibition season, this week felt more like playing for keeps.

On the substantive side, the candidate’s answers and thoughts seemed more fully formed and more clearly expressed. Some of this is just practice. Some of these candidates are new to the big leagues; and veterans such as former Vice President Joe Biden and Sen. Bernie Sanders are getting used to new roles.

Some of the upgrade also seemed attributable to the ABC moderators, all four of whom were crisp. They had challenging questions and they probed in their follow-ups, but they did not intrude on the dynamic among the candidates. Like good referees, they pretty much let the players play — to the benefit of all.

Benefiting most were the candidates who got the most airtime — Biden, Sanders and Sen. Elizabeth Warren.

Much was made of it being the first time viewers had a chance to see Biden and Warren face off — with Sanders, the other candidate consistently in double digits, right there as well. It gave Democratic consumers their best chance for a taste test to date.

Among the three, Warren seemed to make the most of it. She had the freshest energy on stage, and she is getting better at pressing a point. Her share of the airtime this week was nearly 17 minutes — second to Biden, but only by a few seconds. And she was showing passion on a range of outrages rather than intellectual irritation at the way things are.

She also responded to questions and to the answers of her rivals with apparent spontaneity — even when she is recycling what may be a practiced response.

Most observers gave Biden, the putative front-runner, middling marks. For some, he was just OK, a left-handed compliment at best. For others, he was good enough, which isn’t much better. All seemed to agree he wasn’t bad.

It’s hard to know how Biden, soon to be 77, would look to the Democratic electorate based solely on this debate performance, given how long he’s been around. Even more of a factor is the defensiveness many Democrats feel about the guy they still think has the best chance of beating President Trump. But more of that in a moment.

Sanders, who is already 77, came across as every bit his age and just as irascible as he was at just 73 and challenging Hillary Clinton for the last presidential nomination. He once again made a strong case for the national health care system he calls “Medicare for All” — a concept that now gets at least lip service from many of his rivals, as well as pushback from a few.

Even though Sanders’ goal is to make the famous health program available to everybody, it is for now still primarily associated with old folks. It’s likely to be the Democratic Party vehicle for getting to national health care, sooner or later, so it could use –– and likely will have — more age-appropriate champions.

Still, it was Biden’s age that was called into question in this debate, when he had talked about who would qualify under his amendments to Obamacare. Julián Castro, at one end of the stage, objected to what sounded like Biden contradicting himself. When Biden interrupted with a denial, Castro fired back, “Are you forgetting already what you said just 2 minutes ago?”

Without that word “already,” that question might have stood on its own. Instead, it seemed a shot at Biden’s age and past lapses of memory. The audience reacted with a mix of groans and applause. They took it as a shot, and it played as such endlessly on broadcast highlights and in panel post mortems.

Castro may have been the victim of his own need to distinguish himself from the pack, a problem shared by all but the three candidates at center stage. He was anchoring the end of the line-up because his polls and fundraising are barely meeting the criteria for inclusion.

Also in endangered status was the candidate at the other far side of the stage, Minnesota Sen. Amy Klobuchar, who continues to emphasize her “middle of the country” roots and middle of the road positions. Her focus on the middle surely includes the early-caucus state of Iowa, her neighbor to the south, where she needs a break out showing.

Just inside from the two ends onstage were two candidates who were expected to make more noise than either has to date: one was Cory Booker, the senator from New Jersey, a tall and commanding figure who got the night’s best laugh and said many eloquent things on gun violence and the status of his fellow black Americans. The Booker campaign professes to be unworried, but it is hard to fathom why Booker has not broken through in the early states or the national polls.

The same might be said of Beto O’Rourke, the former congressman from El Paso whose campaign has drawn new impetus from last month’s massacre in that city. O’Rourke was saluted by his rivals for his strong stance, and he had a viral moment saying: “Hell yes we’re going to take your AR-15, your AK-47,” referring to the military-style weapons used in many recent mass shootings. That promise, however, does not reflect the position of most of the other candidates, or of the Democratic caucus in the House or the Senate.

Moving in toward the centerpiece trio one found Mayor Pete Buttigieg of South Bend, Ind.,, who used every chance he got to insert thoughtful answers with a fine-chiseled edge. He used his closing remarks to say how much it had meant to his life to come out as gay and marry his husband. The fact that his age, 37, may be more of a weight for his candidacy than his sexuality is one measure of how life in America has changed.

In mirroring status across the stage stood Andrew Yang, a young entrepreneur making a splash with younger voters and casting a wider net with ideas for guaranteed federal income payments (in lieu of other programs) and 100 Democracy Dollars to supplant lobbyists’ actual dollars.

Which leaves us with Kamala Harris the one candidate who stood aside from the threesome at center-stage but was not part of the trio on either wing. The California senator tried a good-natured jab at Biden regarding his oft-repeated ties to President Obama. It worked in its way, especially with the crowd at Texas Southern University, a historically black school. But it didn’t have nearly the bite of her June debate challenge to Biden for his opposition to busing for school integration in the 1970s.

One thing Harris succeeded in doing was returning the debate, again and again, to the subject of Donald Trump. One after another, the candidates would acknowledge that beating Trump was everyone’s ultimate goal, an existential necessity for the party and the over-arching unifying element in this contest.

Yet, curiously, not one candidate mentioned the impeachment debate currently raging within the House of Representatives, where most Democrats now want a formal impeachment proceeding but Speaker Nancy Pelosi does not – at least yet.

Neither did anyone in the debate mention the recession jitters that polls show many Americans feeling, if only because the length of the current expansion and indications it may be ending.

That’s important, because recessions beat incumbent presidents more often than the opposing party’s nominee does. No incumbent lost between the Depression election of 1932 and 1976, when Democrat Jimmy Carter talked of an “economic misery index” in ousting Republican Gerald Ford. That same index was even worse when Ronald Reagan ousted Carter four years later.

George H. W. Bush also lost as an incumbent in 1992, the victim of a brief recession and an independent candidate (Ross Perot) who got 19% of the popular vote. Since then, three incumbent presidents have been re-elected and none has lost, despite the efforts of well-known, well-financed and party-backed challengers (Robert Dole, John Kerry and Mitt Romney).

That is largely why polls taken this week by CNN and by NPR/PBS NewsHour/Marist found a plurality of Americans expect Trump to win a second term, even though far fewer think he deserves it. Trump’s approval number is now among the lowest ever for presidents after 20 months in office. But some have come back from comparable low points, including Obama and Reagan (who came back to win 49 states).

It’s going to take more than good debate performances, and more than winning the nomination, for one of these Democratic contenders to defeat this incumbent. Only bad economics, or the actions of the incumbent himself, are likely to accomplish that.

But to make themselves attractive as a reasonable option, the Democrats need to present coherent, clear alternatives in policy and persona. This week’s debate was at least a longer step in that direction.