Biden shared the platform at Detroit's Fox Theatre on Wednesday with senators Kamala Harris, Cory Booker, Michael Bennet and Kirsten Gillibrand, New York Mayor Bill de Blasio, former Housing Secretary Julian Castro, Washington State Governor Jay Inslee, congresswoman Tulsi Gabbard and Businessman Andrew Yang.
On stage, Biden was pounced on when the conversation turned from healthcare to immigration, Efe news reported.
Castro, who was a part of the Obama Cabinet along with Biden, defended decriminalizing the entry of undocumented immigrants to the US, which the former Vice President is opposed to.
"If you elect me President, you're electing me not to follow. You're electing me to lead," Castro said. "And open borders is a right-wing talking point, and frankly, I'm disappointed that some folks on this stage have taken the bait."
Biden then took direct aim at Castro, saying: "I found that Julian, excuse me, the Secretary, we sat together in many meetings. I never heard him talk about any of this when he was the Secretary."
"If you cross the border illegally, you should be able to be sent back," Biden added. "It's a crime."
Castro replied: "It looks like one of us has learned the lessons of the past. One of us hasn't."
The Texan then said that there still ought to be consequences if one crosses the border without authorization, but the penalties should be civil.
"I have guts enough to say his plan doesn't make sense," Biden retorted.
De Blasio then reproached Biden for the number of deportations of undocumented immigrants during the Obama administration, higher than those of the current President, Donald Trump, during the first two years of his term.
"I was Vice President ... not the President. I keep my recommendation in private, unlike you. I expect you would go ahead and say whatever was said privately with him. That's not what I do," Biden said, while underlining that Obama tried to find a way to grant citizenship to the beneficiaries of Deferred Action for Childhood Arrivals (DACA).
Approved in 2012 by Obama, DACA has curbed the deportation of some 750,000 undocumented people who entered the country as children, and referred to as "Dreamers."
Booker was next to join the bandwagon of critical voices against Biden.
Immigration then gave way to justice when Booker pinned down Biden over the 1990 Criminal Justice Act, which he helped enact, and which is now regarded as the source of mass incarceration, particularly of racial minorities.
Biden was also set upon for his current and past positions on climate crisis, trade agreements, racial discrimination and abortion.
Harris, who scores highly in polls and did well in the first debate in June, this time did not make much of a mark and even received attacks from Gabbard for her stint as California's Attorney General.
"There are too many examples to cite but she put over 1,500 people in jail for marijuana violations and then laughed about it when she was asked if she ever smoked marijuana," Gabbard said.
Wednesday marked the conclusion of the second Democratic presidential debate, after the 10 other candidates - among them progressive senators Bernie Sanders and Elizabeth Warren - took part in the first round on Tuesday.
( With inputs from IANS )