Todd Graham is the director of debate at Southern Illinois University. His debate teams have won five national championships and he has been recognized three times as the national debate coach of the year. Follow him on Twitter . The views expressed in this commentary belong solely to the author. View more opinion at CNN.

(CNN) As a debate coach, the most common question I get asked is this: In the Democratic field, who can stand up to President Trump in a debate?

Last night's performance gave us at least one clear answer to that question. The candidates' debate grades say it all.

A+

Elizabeth Warren

Warren hit all the right notes with her tone, demeanor, language choices and especially her policy-specific answers. She struck the right balance between progressive and pragmatic while pounding away at corporations, the rigged system, greed by insurance and pharmaceutical companies and more.

I first realized Warren was owning the debate stage at the onset of the event -- actually, during a mistake she made. She decided to begin an anecdote about Ady Barkan, a man with ALS who was being failed by a broken health care system. Unfortunately, Warren ran out of time to tell the whole story. But, on her next speaking turn, she continued the anecdote to some mild chuckles from the audience. What she did next was perfect. She looked at the audience and said, "This isn't funny. This is somebody who has health insurance and is dying."

Todd Graham

She lectured the audience and didn't give a damn what they thought. And she continued dominating throughout the evening.

To Delaney: "I don't understand why anybody goes to all the trouble of running for president of the United States just to talk about what we really can't do and shouldn't fight for."

To the voters: "We can't choose a candidate we don't believe in just because we're too scared to do anything else... Democrats win when we figure out what is right and we get out there and fight for it. I am not afraid. And for Democrats to win, you can't be afraid, either."

To everyone: "We need to call out white supremacy for what it is: Domestic terrorism."

Importantly, Warren's policy answers also were the best on stage, with her explanations of why we must change the immigration laws (because we shouldn't ignore laws) and how a no first-use policy on nuclear weapons will make a safer world. My own debate teams have won countless rounds on this very argument.

B+

Bernie Sanders

Sanders was clever to use the word "radical" when reminding us his health care plan isn't as crazy as many make it out to be. It's in fact used successfully by other countries, including Canada. Sanders' rhetoric was also compelling when he reminded everyone that Republicans aren't afraid of big ideas, so Democrats shouldn't be either.

And while he took some hits on removing Americans' choices from health insurance and the potential effects of providing undocumented immigrants with free health care and education, Sanders' defense was generally successful.

B

Pete Buttigieg

Buttigieg's idea that military action needs three-year sunset clauses, forcing Congress to regularly reevaluate our involvement overseas was brilliant -- especially coming from a veteran. And he's getting good at calling out hypocrites in the Republican party who stand for party over country when supporting Trump. His advice that Democrats should not worry about being called socialists was spot-on.

Unfortunately, Buttigieg failed to distinguish his ideas from Warren's or Sanders' on issues such as debt-free college. And he lacked the fire of some of the other candidates.

Beto O'Rourke

O'Rourke gets "most improved" from his previous debate. Most of his answers were clear and concise. But when asked how to beat Trump, O'Rourke offered nothing more than what we saw from him in his battle for the Texas Senate -- a battle in which he was defeated. Democratic voters must be shaking their heads in disbelief that O'Rourke thinks the same strategy that lost to Ted Cruz can somehow beat Trump.

C+

Amy Klobuchar

Klobuchar wasn't as specific, memorable, or personable in this debate. And it began with an opening statement that was all over the place. While she occasionally had good points, like calling out Trump's criticism of Baltimore, she was often missing in the debate (perhaps due to the moderators not calling on her enough).

C

Steve Bullock

Bullock's strength was moderation. He successfully criticized "wish-list economics" and was believable when he talked about workers and farmers losing money when Trump tweets about trade. Unfortunately, he failed to defend a clear position on nuclear weapons, with a muddled and confusing answer in which he said, "Never, I hope, certainly in my term or anyone else, would we really even get close to pulling that trigger."

C-

Tim Ryan

Ryan was partially successful in his pragmatic approach to answering questions. But some lines seemed forced, as when he said to Bernie Sanders, "You don't have to yell." Heck, Sanders was actually pretty calm (for Bernie) at the time. Plus, Ryan's Ted Talk-esque conclusion about not capturing the left or center lane but instead capturing the viewers' imaginations was so contrived it made me laugh out loud.

D+

John Delaney

With a better stage presence than he had in the previous debate, Delaney improved. And he made some sound points about finding realistic climate policies. He was actually holding his own on that issue until attention turned to Elizabeth Warren. Unfortunately, Delaney was outdone by Warren's on-point and number-specific climate response. Nice try for Delaney, but he was upstaged in the end.

D

John Hickenlooper

He didn't stick to his strongest arguments like he did in the previous debate when he constantly pointed to examples of his successful governorship. Hickenlooper was unfocused in many of his answers, from saying "there is a way of looking at trade that is therapeutic," to mumbling something about "big, you know, noisy hangars" when discussing American military foreign policy. Plus, his lack of energy was noticeable compared to others on stage.

D-

Marianne Williamson

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The problem with Williamson in this debate is that for every legitimate criticism of our government she gave -- and there were several -- she lacked follow-up solutions. She derided the "political insider game and wonkiness and intellectual argument," without offering a clear picture of her practical alternative. And her closing statement was something about emotional and psychological gobbledygook that finished with a crescendo like she was singing the big finale of a Broadway musical.