(CNN) The latest Democratic debate threw up a rich haul of clashes, incidents, slow burning controversies and policy collisions that will help define the 2020 race in the weeks to come.

Often, a debate's impact only becomes clear in subsequent days, when exchanges that did not immediately resonate take on extra significance as the churn of the campaign does its work.

There's a trove of material for each campaign to mine to tweak the weaknesses of rival candidates. And President Donald Trump's team must have been watching with glee as comment on guns and health care piled up material for general election attack ads.

Over the span of this race, there's little evidence that the debates are changing the hierarchy of candidates. But the confrontations are serving to expose the complex layers of the campaign and offer clues over how it may turn out.

The top tier may freeze in place

The debate solidified the clear top tier in this race and none of the leading candidates looks likely to quickly fade in the crucial run-up to the Iowa caucuses in February.

Former Vice President Joe Biden had a patchy night but Thursday was his best performance so far in his campaign. Sen. Elizabeth Warren was relatively quiet but made no huge mistakes. And Sen. Bernie Sanders will have delighted his solid supporters but did not seem to solve the riddle of broadening his base.

These three however have yet to turn their full fire on one another. That's one thing to watch for as the race really gets going.

Outsider desperation

From here on in, the clock is ticking for everyone else.

Low polling candidates must elbow themselves into the top tier. Julian Castro's unsubtle jabs at Biden's age, Beto O'Rourke's vow to confiscate assault rifles and an overt turn against Trump by Kamala Harris in a direct-to-camera stare down are a sure sign the pressure to stand out is beginning to show.

In the weeks to come, keeping the cash flowing will become even more important as candidates build early state machines and buy advertising. So they must show donors that they still have a shot and there's a reason to go on. A metric of success for this debate will come in third quarter fund raising data at the end of the month.

Businessman Andrew Yang rolled out a novel way of getting some buzz, turning his campaign into a raffle to give 10 people $1000 a month for a year to highlight his universal basic income plan.

Biden and the age issue

Castro's pile-on was clumsy . By repeatedly asking Biden: "Are you forgetting what you said two minutes ago?" the former HUD Secretary actually built empathy for the former vice president.

But make no mistake, many of the other candidates are happy this is out there and even happier that Castro stepped on the landmine before they had to -- their post-debate interviews are proof of that.

"There's a lot of people concerned about Joe Biden's ability to carry the ball across the end line without fumbling," Booker told CNN's Anderson Cooper after the debate. Harris was asked several times on "New Day" about the Castro assault, but pointedly chose not to criticize its author or to defend Biden.

The question of whether the former vice president is fit for the rigors of the presidency and to take on Trump is not going away. It's one of his biggest weaknesses and, as even Biden has said, it's fair game for opponents to explore. And Biden put it on the table himself by rooting his campaign in an argument about electability.

Any stumbles in the Democratic debate next month and the issue will be back on the front burner.

Moderates awake

The dominant narrative is that this race is taking Democrats, led by Sanders, Warren and the activist base, so far left that they risk alienating America's political middle.

Biden, Harris, South Bend, Indiana, Mayor Pete Buttigieg, Sen. Amy Klobuchar and O'Rourke all had strong moments pushing a pragmatic brand of politics to reflect Washington realities.

Their strategy is likely to become a more overt theme in the contest as the first nominating voting looms.

The schism in the field is especially evident on health care -- broadly over whether to build on Obamacare or to go all in on a Medicare for All push.

There are signs that Warren might be hedging her bets and trying to provide herself room to track back toward the center in a general election campaign. But her line that "I have never met anyone who likes their health insurance company" may put off Americans who don't want to give up employer-provided plans.

It will certainly be highlighted by Trump if she ends up as his Democratic opponent and will reinforce claims by the moderates that progressives are leading Democrats into a dead end.

O'Rourke on guns: Brave move or historic error?

Another moment from Thursday sure to find its way into an attack ad is O'Rourke's vow: "Hell, yes, we're going to take your AR-15, your AK-47." His call for a mandatory guns buy back scheme was an impassioned reaction to a massacre in his home town of El Paso and a strategy designed to help his underperforming campaign grab the spotlight.

There's an argument that gun politics is changing and Washington is yet to get the message. But O'Rourke also risks playing into GOP dogma that all gun control is a ruse for Democrats to confiscate the guns of law abiding Americans. It's a base-stoking claim already burning up conservative media. And the eventual Democratic nominee will have to repeatedly answer for O'Rourke's comment.

One prominent Democrat is already mad at O'Rourke.

"I frankly think that that clip will be played for years at Second Amendment rallies with organizations that try to scare people by saying, 'Democrats are coming for your guns,'" Delaware Sen. Chris Coons said Friday on CNN's "Newsroom."

The Trump in the room

The Democratic debate at times seemed from another era. Candidates earnestly clashing over policy, pursuing traditional political attacks and firing off pre-planned zingers.

Trump blew up such conventional political codes in destroying the GOP field in 2016. Assuming he shows up for presidential debates next fall, whoever emerges from the Democratic race will have to deal with the President's brawling, outlandish style.

While Democrats were quarreling over the nuances of health care, Trump counter-programmed with a whirling campaign pitch at a Republican retreat in Baltimore. He vented against bans of plastic straws, complained about energy saving light bulbs Trump claimed made him look orange and included a bizarre aside about Republican House Minority leader Kevin McCarthy.

"Kevin is just like a cow, he's just smaller," Trump said.

Overall, the Democratic presidential race marks an implicit bet that Americans are tired of Trump's act -- and that offering clear plans on issues like health care is an antidote to the craziness that rocks the White House every day.

Biden has made the most obvious pitch so far for the role of Trump slayer. Harris joined the game on Thursday night meaning that the question of electability will be increasingly important in the weeks to come.