The topic of immigration was, once again, a major point of contention during the fourth Democratic debate, with former Vice President Joseph R. Biden Jr. under attack from hecklers as well as his fellow Democrats over the Obama administration’s deportation record.

Asked whether he would resume President Barack Obama’s deportation rate — which outpaced the first two years of the Trump administration — Mr. Biden said, “Absolutely not.” But he defended Mr. Obama’s record.

“To compare him to Donald Trump, I think, is absolutely bizarre,” he said.

The exchange over immigration began when Julián Castro, who served as Mr. Obama’s housing secretary, defended his proposal to decriminalize border crossings, which he has called the only way to end the Trump administration policy of separating children from their parents at the border.

[Read more about the plan to decriminalize crossing the border.]

Mr. Biden — who seemed to raise his finger during the June debate to indicate he favored Mr. Castro’s plan — has since disavowed that position.