What Were the Most Memorable Moments From Last Night’s Debate?

At their best, they were clever and unscripted. A timely comeback. A witty one-liner.

At their worst, they were robotic and rambling. Clumsy. Cringe-worthy.

Here are some of the most memorable moments from Wednesday’s Democratic presidential debate in Atlanta, hosted by MSNBC and The Washington Post.

Senator Kamala Harris of California said President Trump had compromised the checks and balances on North Korea’s nuclear capabilities with his unilateral dealings with the country’s leader, Kim Jong-un.

She said Mr. Trump was the greatest threat to the national security of the United States, pointing to his decision to withdraw from the Paris climate agreement and the Iran nuclear deal, as well as his decision to pull American troops from Northern Syria.

Senator Elizabeth Warren of Massachusetts opened the debate by saying Gordon D. Sondland, the United States ambassador to the European Union, had no qualifications other than his $1 million contribution to President Trump’s inaugural committee.

Ms. Warren said Mr. Sondland’s testimony during an impeachment proceeding in the House of Representatives on Wednesday added to the mounting evidence that President Trump had tied foreign aid to Ukraine to an investigation of former Vice President Joseph R. Biden Jr.’s son.

Mayor Pete Buttigieg of South Bend, Ind., said that Mr. Trump was not putting critical military resources into things like artificial intelligence for border security.

Senator Amy Klobuchar of Minnesota avoided a direct attack on Mr. Buttigieg when asked about her comment that a woman with his credentials would not be doing as well as a candidate. But Ms. Klobuchar did not shrink from the moment of getting a point across that women candidates are treated differently.

Senator Cory Booker of New Jersey created a buzz with his dig at Mr. Biden, who recently said he opposed the legalization of marijuana. Mr. Booker said Mr. Biden’s position on cannabis was at odds with the progressive wing of the Democratic Party and many black Americans, who he said have been disproportionately hurt by criminal charges related to marijuana.

Andrew Yang, the former tech executive and entrepreneur, was asked what he would say to Vladimir Putin in their first conservation if elected president. Mr. Yang answered that he would tell the Russian president that his “days of meddling in American elections are over.”

Mr. Biden quipped about a recent swipe at him by Mr. Kim, as quoted by North Korean state media. Senator Bernie Sanders of Vermont then interjected, “Other than that, you like him,” which drew laughs from the candidates and audience.

Mr. Biden used the wrong metaphor as a point of emphasis when asking what he would do to address the culture of violence toward women in the United States.

He started his answer by urging Congress to reauthorize the Violence Against Women Act, which Mr. Biden championed when he was a member of the United States Senate.

Mr. Biden, who has enjoyed strong polling numbers among black voters, rattled off a list of endorsements of prominent African-American lawmakers and said there was reason that his appeal transcended racial lines. But Mr. Biden flubbed the number of black women who have served in the Senate: there have been two. He was endorsed by former Senator Carol Moseley Braun of Illinois, the first black woman elected to the chamber.

The second, Ms. Harris, was onstage to his left.

Isabella Grullón Paz contributed reporting.