Other candidates challenge Biden

Joe Biden had to fend off attacks on Wednesday during a Democratic presidential primary debate about his stances on healthcare, immigration and criminal justice, as several Democrats trailing in the polls looked to increase their standing.

Ten candidates faced off in Detroit, Michigan, one night after 10 other Democratic hopefuls clashed on the same theater stage.

US Senator Cory Booker of New Jersey, in calling out the former vice-president for favoring giving visas to "PhDs", said it was that type of division on immigration that Republicans were supporting. Booker also chastised Biden for invoking " (former) president (Barack) Obama more than anyone in this campaign".