Second Democratic debate: Joe Biden attacked by rivals during tricky night for front-runner

Joe Biden fended off sustained attacks by his Democratic presidential rivals on Wednesday as he was repeatedly challenged over his past record and suffered a number of verbal slip-ups that marred his performance.

The former US vice president and front-runner was accused of "dipping into the Kool-Aid" when defending his criminal justice record and hiding behind Barack Obama's reputation as those on the debate stage ganged up against him.

Kamala Harris, the California senator, sparred with Mr Biden on healthcare and - like last month - his race record, while Cory Booker, the New Jersey senator, accused him of "phony" tough-on-crime rhetoric in the past.

Bill de Blasio, the New York mayor, signposted his determination to challenge Mr Biden by naming him in his opening remarks and asked three times why he did not stop the mass deportations of immigrants in the Obama years.

Mr Biden largely fought off the attacks and his performance was a marked improvement after the hammering he took at last round of debates, critics said.

He stayed true to his pledge to be less "polite" in this debate, accusing Ms Harris and others supporting government-funded healthcare for having bad "math" and claiming the attacks on him were politically motivated.

However, a number of embarrassing stumbles during the second presidential debate will likely force the spotlight back onto Mr Biden's age. He would be 78 on inauguration day 2021 if he becomes president, the oldest person ever elected to the job.

At one point while debating Mr Booker, Mr Biden referred to his rival first as "president" and then "future president" before correctly calling him "senator". Mr Booker thanked him for his endorsement in jest.

In his closing comments Mr Biden, like other candidates, appeared to promote his website as he urged supporters to "go to Joe 30330" and back him. Yet that was not a website but a phone number which supporters can text.

Those slip-ups, combined with a delivery style that was occasionally faltering - he pulled himself up mid-flow a handful of times - may well be jumped on by Donald Trump and his supporters who have dubbed him "Sleepy Joe".

The focus on Mr Biden reflects the fact that for the last three years he has consistently led polls of who Democrats want to lead them into the November 2020 election, though his lead has shrunk in recent weeks. 

By focusing on Mr Biden's past record, rivals appeared to be attempting to portray him as out of step with party activists looking for bold change, while also generating made for TV 'moments' that can help them standout from a crowded field.

Mr Booker, an African-American senator who continues to poll in the low single figures, created one of the standout clashes of the night as he took on Mr Biden's record of criminal justice in a five-minute back and forth.

The pair have been trading blows for weeks leading up to this debate in Detroit, with Mr Booker calling his rival the "architect of mass incarceration" and the Biden camp questioning Mr Booker's record while mayor of Newark.

Mr Booker said he was "shocked" that Mr Biden wanted to compare records, zoning in on the front-runner's role in passing major crime bills that he blamed for leading to a soaring prison population, especially affecting African-Americans.

When Mr Biden said Mr Booker had adopted a "zero tolerance policy on stop and frisk" in Newark, the latter shot back: "Mr Vice President, there's a saying in my neighbourhood - you’re dipping into the KoolAid, you don’t even know the flavour.”

Mr Booker went on: "There are people right now in prison for life for drug offences, because you stood up and used that tough on crime phony rhetoric that got a lot of people elected, but destroyed communities like mine."

More high profile clashes came between Mr Biden and Ms Harris, whose decision to question his past willingness to work with segregationists in the US Congress at the first round of debates last month earned her a jump in the polls.

Mr Biden, 76, made clear he anticipated more attacks, telling Ms Harris, 54, as they shook hands at the start of the debate: "Go easy on me, kid."

Within minutes the pair were debating healthcare, with Mr Biden criticising Ms Harris's number of high profile clarifications over exactly where she stood on the issue earlier this year.

"To be very blunt and to be very straight forward, you cannot beat Donald Trump with double talk," Mr Biden said. He warned that Ms Harris's plan to give everyone government-funded healthcare could cost more than $30 trillion.

Ms Harris in turn criticised Mr Biden's plan for leaving an estimated 10 million Americans uninsured, adding: "I think that you should really think about what you are saying."

The pair also returned to Mr Biden's past opposition to busing, the policy of transporting children of different races by bus to break down school segregation.

Mr Biden questioned why Ms Harris, when she was California's attorney general, had a police department that was "abusing people's rights" and claimed she had not done enough to segregate schools herself. Ms Harris said she had spent time "cleaning up the consequences" of legislation Mr Biden passed in the Senate.

The exchanges highlighted the difficulties Mr Biden has in defending a record in Congress and the White House that stretches back almost five decades, given the vast changes US society has gone through over that period.

Mr Biden was criticised at one point as he attempted to explain away the high numbers of migrant deportations during the Obama presidency, saying under repeated grilling that he was "not the president" at the time.

Mr Booker leaped on the comment, saying: "Mr Vice President, you can't have it both ways. You invoke President Obama more than anybody in this campaign. You can't do it when it's convenient and then dodge it when it's not."

Mr Biden was not the only leading candidate put in the spotlight by rivals, with Ms Harris told she must apologise for jailing people who used marijuana while she was in office in California by congresswomen Tulsi Gabbard.

Yet it was the collective grilling of the former vice president and his verbal blunders that will likely be the focus of the cable news coverage in the coming days.

The next debate in September will feature a much smaller number of candidates given the stricter qualifying criteria. Voting for the Democratic presidential nominee begins in February 2020.