HOUSTON (AP) — Joe Biden parried attack after attack from liberal rivals Thursday night on everything from health care to immigration in a debate that showcased profound ideological divides between the Democratic Party’s moderate and progressive wings.

The prime-time debate also elevated several struggling candidates, giving them a chance to introduce themselves to millions of Americans who are just beginning to follow the race.

Biden dominated significant parts of the evening, responding strongly when the liberal senators who are his closet rivals — Bernie Sanders and Elizabeth Warren — assailed him and his policies.

Unlike prior debates, where Biden struggled for words and seemed surprised by criticism from fellow Democrats, he largely delivered crisp, aggressive responses. He called Sanders “a socialist,” a label that could remind voters of the senator’s embrace of democratic socialism. And Biden slapped at Warren’s proposed wealth tax.

A two-term vice president under Barack Obama, Biden unequivocally defended his former boss, who came under criticism from some candidates for deporting immigrants and not going far enough on health care reform.

“I stand with Barack Obama all eight years, good, bad and indifferent,” Biden declared.

The candidates debated with polls showing a strong majority of voters believe the country is headed in the wrong direction under the first-term Republican president’s leadership. But nine months into their nomination fight, divided Democrats have yet to answer fundamental questions about who or what the party stands for beyond simply opposing President Donald Trump.

The party’s 2020 class, once featuring two dozen candidates, has essentially been cut in half by party rules requiring higher polling and fundraising standards for debates. Just 10 candidates qualified for Thursday’s affair, though more have qualified for next month’s round.

Those in the second tier, after Biden, Warren and Sanders, are under increasing pressure to break out of the pack. They all assailed Trump.

New Jersey Sen. Cory Booker called Trump a racist. Former Texas Rep. Beto O’Rourke called him a white supremacist. And Kamala Harris, a California senator, said Trump’s hateful social media messages provided “the ammunition” for recent mass shootings.

In addition to Trump, Biden’s rivals also turned against Obama’s legacy at times as they sought to undermine the former vice president’s experience.

Sanders insisted that Biden bears responsibility for millions of Americans going bankrupt under the “Obamacare” health care system. Castro raised questions about the Obama-Biden record on immigration, particularly the number of deportations that took place.