Twenty Democratic presidential candidates had their first chance to square off on the same stage this week. A handful of them took steps that could help them stand out in the jammed field — while others struggled or gained little ground on a crowded debate stage. Some of the race's early leaders met expectations as contenders. Candidates such as Sen. Elizabeth Warren, D-Mass., and South Bend, Indiana, Mayor Pete Buttigieg earned plaudits in surveys and from pundits. Others also had performances during the Wednesday and Thursday night debates that made them stand out — for better or worse. A strong debate performance can help to propel a candidate with donors and media coverage, but it hardly guarantees a surge or sustained success in a primary. On the other hand, one poor performance does not necessarily deter a candidate's campaign — especially if they come into the debate with strong support. Here are five of the candidates that both post-debate polls and pundits identified as the winners and losers of the two nights of debate in Miami.

Winner: Kamala Harris

Sen. Kamala Harris (D-CA) speaks during the second night of the first Democratic presidential debate on June 27, 2019 in Miami, Florida. Drew Angerer | Getty Images

Harris took swings at President Donald Trump early in Thursday night's debate. She criticized the Republican tax plan and his immigration policy. But she created the most memorable moment of either night when she targeted a Democratic rival. The senator from California criticized former Vice President Joe Biden — the primary's early frontrunner — over his record on race and the desegregation of school busing in personal terms. "There was a little girl in California who was part of the second class to integrate her public schools, and she was bused to school every day, and that little girl was me," Harris said. She called his comments about working with segregationist senators "hurtful." In a tweet, Democratic presidential candidate John Delaney called Harris' criticism of Biden an "incredible moment." Delaney tweet: Incredible moment from Senator @KamalaHarris. The decisions elected officials make impact people's lives directly and her story brought that home. This is what public service is about. Lynn Vavreck, a professor of American politics and public policy at UCLA, called the moment "among the more amazing things I have seen in a political debate." She added that Harris "had an amazing night." Searches on Google for "busing" spiked more than 3,000% after the senator brought up the issue, according to Google Trends. At one point during the debate, Harris was the top trending topic on Google across the U.S. One quantitative measure backed up Harris' reviews. Support for the senator among likely Democratic voters spiked to 16.6% after Thursday, up from 7.9% before the first debate, according to Morning Consult polling done for FiveThirtyEight. Her net favorability rating — favorable minus unfavorable views of the senator — jumped by 9.2 percentage points. Biden, for his part, said Harris mischaracterized his record on race. He said he worked as a public defender instead of a prosecutor, which Harris was as district attorney in San Francisco and attorney general in California.

Winner: Julian Castro

Democratic presidential hopeful former US Secretary of Housing and Urban Development Julian Castro speaks during the first Democratic primary debate of the 2020 presidential campaign season hosted by NBC News at the Adrienne Arsht Center for the Performing Arts in Miami, Florida, June 26, 2019. Jim Watson | AFP | Getty Images

"I think that you should do your homework on this issue," Castro said to fellow Texan and former Rep. Beto O'Rourke after a heated exchange on whether the U.S. should decriminalize immigration. The Obama administration's Housing and Urban Development secretary started the night's discussion on immigration by saying a photo of a drowned father and 23-month-old daughter trying to gain asylum in the U.S. should "piss us all off." He ended the night with the fourth-most speaking time out of the 10 participants, according to The Washington Post.

Castro entered the night as a relative unknown: Only about 39% of likely Democratic voters had an opinion of him entering the night, Morning consult found. But after the debates, 47.8% of respondents had a favorable view of him, versus only 11.7% who had an unfavorable opinion. His net favorability rating increased 16.1 percentage points, more than even Harris' did. In addition, 1.7% of likely Democratic voters said they would vote for him following the debates, versus only 0.7% before it.

Winner: Cory Booker

Democratic presidential hopeful US Senator from New Jersey Cory Booker participates in the first Democratic primary debate of the 2020 presidential campaign season hosted by NBC News at the Adrienne Arsht Center for the Performing Arts in Miami, Florida, June 26, 2019. JIM WATSON | AFP | Getty Images

Booker has found himself outside the top tier of contenders in most early primary polling. He made his presence known on Wednesday night. The senator from New Jersey talked about how "this economy is not working for average Americans." He tried to fight off accusations that he is too friendly to drug companies by promising to hold opioid makers criminally liable for their role in an addiction and overdose crisis. By the end of the night, Booker talked more than any other candidate. His net favorability rating jumped by 8 percentage points — nearly as much as Harris rose, according to Morning Consult. Still, backing for Booker barely changed in the survey: only 2.8% of respondents said they would support him following the debates, about unchanged from 3% before the candidates shared the stage.

Loser: Beto O'Rourke

Former U.S. Rep. Beto O'Rourke speaks at the first U.S. 2020 presidential election Democratic candidates debate in Miami, Florida, U.S., June 26, 2019. Mike Segar | Reuters

Many experts considered the immigration spat with O'Rourke as Castro's signature moment Wednesday. On a night where few candidates faced personal attacks, O'Rourke also found himself targeted for his health-care stance. When the former congressman argued against eliminating private insurance, New York Mayor Bill de Blasio jumped in to say the system "is not working for tens of millions of Americans." Only Booker talked more than O'Rourke on Wednesday, according to the Post. But O'Rourke's net favorability dropped 4.3 percentage points, the most among all the candidates on stage Wednesday, according to Morning Consult. After the debate, 2.2% of respondents said they would vote for O'Rourke, down from 3.6% before. During a conference call with O'Rourke on Thursday, his donors discussed how he could improve in the next debate.

Loser: Joe Biden

Democratic presidential candidate former Vice President Joe Biden speaks during the second night of the first Democratic presidential debate on Thursday, June 27, 2019, at the Arsht Center for the Performing Arts in Miami. Al Diaz | Miami Herald | Tribune News Service | Getty Images