Warren was the front-runner of the first night with Bernie Sanders, Joe Biden, Kamala Harris and Pete Buttigieg all randomly selected to appear during night two of the first round of Democrat debates.
"When you've got a government, when you have an economy that does great for those with money and is not doing great for everyone else, that is corruption, pure and simple", the U.S. senator and former Harvard law professor added. "We can make it work for everyone", she said.
Still, despite his baffled reaction to O'Rourke, Booker wasn't about to let his debate opponent be the only Spanish-speaker on the stage.
De Blasio, a late entrant to the race, earned loud applause when he reminded citizens immigrants were not their enemies.
"There's three women up here who have fought pretty hard for a woman's right to choose", Klobuchar shot back.
Mr O'Rourke also came under attack from Castro over the separation of families and detention of migrants at the southern border.
Sen. Elizabeth Warren says she would go after the big fundraisers who carry so much power in Washington.
The Democratic candidates range from senators to state representatives to former Presidential cabinet members to entrepreneurs.
Earlier in the evening, Trump posted a single word tweet in all caps - "BORING" - seemingly addressing the first of two debates where the top Democratic presidential hopefuls discuss issues like health care, immigration and gun control.
The debate began at about the same time that Air Force One, carrying Trump and his entourage to Japan, stopped to refuel at Joint Base Elmendorf-Richardson in Anchorage, Alaska. It's doing great for giant drug companies.
There are several ways to watch tonight's Democratic Presidential Debate, including new ways to live stream the debates in 2019.
The president had already predicted he'd find the debate "boring", telling Fox Business Network earlier in the day: "It just seems very boring, but I'm going to watch it because I have to".
Congresswoman Tulsi Gabbard savaged Trump on foreign policy, saying his "chickenhawk cabinet" has "led us to the brink of war in Iran".