WASHINGTON (Reuters) - Former President Barack Obama was not on the Democratic presidential candidate debate stage on Wednesday night, but he was omnipresent as 2020 hopefuls grappled with the legacy of their party’s most popular member.

Coming under heavy attack from more liberal, lower-polling candidates, front-runner Joe Biden frequently invoked Obama in his defense. Biden served eight years as No. 2 to the first black U.S. president.

Obama enjoys wide popularity not just in his party, but among all Americans, including blacks, whose backing is crucial to win the Democratic nomination to take on Republican President Donald Trump in the November 2020 election. In a 2018 poll by the Pew Research Center, more than four in ten respondents named Obama as the best president of their lifetime.

That left some of Biden’s rivals in the Democratic nominating contest struggling to find a way to criticize the former vice president and his pledge to build on Obama’s accomplishments, while avoiding disparaging the former president directly.

Several candidates on the debate stage on Wednesday, such as U.S. Senators Kamala Harris and Cory Booker and New York Mayor Bill de Blasio, questioned aspects of Obama’s record, suggesting that at least some in the party had moved on from his tenure.

Harris took a swipe at what some consider to be Obama’s greatest achievement, the Affordable Care Act, popularly known as Obamacare, arguing it was not stopping insurance companies from profiting.

She criticized Biden for his healthcare plan, which would augment Obamacare.

“Senator Biden, your plan will keep and allow insurance companies to remain with status quo, doing business as usual, and that’s going to be about jacking up co-pays, jacking up deductibles,” said Harris, who has proposed a Medicare for All system that would all but eliminate private insurance and largely supplant Obama’s program.

Democrats have made access to affordable healthcare a defining issues as the Trump administration has worked to chip away at Obamacare.

At a rally in Cincinnati on Thursday night, Trump weighed in on the debate comments, saying: “The Democrats spent more time attacking Barack Obama than they did attacking me practically.”

‘BIZARRE’

FILE PHOTO: Former U.S. President Barack Obama addresses a town hall of young leaders from across Europe at an Obama Foundation event in Berlin, Germany April 6, 2019. REUTERS/Fabrizio Bensch

On Thursday, Harris, who with Booker is a prominent black presidential contender, was careful to stress she was not impugning Obama. Speaking to reporters in Detroit, she said she has “nothing but praise for President Obama.”

“I think he did great work. Many presidents before him tried to reform America’s healthcare system. He actually got it done,” she said.

At Wednesday’s debate, Booker and de Blasio pressed Biden to defend the Obama administration’s large number of deportations of immigrants who were in the country illegally. Without commenting on the policy, Biden refused to tell de Blasio how he advised the president at the time.

“I was vice president. I am not the president. I keep my recommendation to him in private,” Biden said. “Unlike you, I can expect you would go ahead and say whatever was said privately with him. That is not what I do.”

At one point, Biden seemed incensed at de Blasio’s attacks on Obama’s policies.

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

But Biden made clear he too parted ways at times with Obama, saying he disagreed with increasing troop numbers in Afghanistan.

Booker argued that Biden only tied himself to Obama when it suited him.

“You can’t have it both ways,” Booker said. “You invoke President Obama more than anyone else in this campaign. You can’t do it when it’s convenient and then duck it when it’s not.”

RISKY BUSINESS

At a campaign stop in Detroit on Thursday, Biden said the drumbeat of criticism of Obama surprised him.

“I’m proud of having served with him,” Biden said. “I’m proud of the job he did. I don’t think there is anything he has to apologize for and it kind of surprised me the degree of criticism.”

Obama has largely stayed silent since leaving office in 2017, opting not to endorse anyone in the Democratic field and only occasionally weighing in to criticize Trump. But it remains possible he will campaign next year for the Democratic nominee.

Eric Holder, who served as U.S. attorney general under Obama, delivered a frank warning on Wednesday to Democrats who critique the president.

“To my fellow Democrats. Be wary of attacking the Obama record. Build on it. Expand it. But there is little to be gained - for you or the party - by attacking a very successful and still popular Democratic President,” Holder wrote on Twitter.

Speaking to MSNBC on Thursday, Booker said Obama’s record was fair game.

“President Obama has been the statesman of our party and has the highest approval ratings, but I don’t think that any administration ... is without criticism,” he said.

Quentin James, co-founder of The Collective PAC, which favors a presidential ticket that would include Booker or Harris, said progressives could build on Obama’s accomplishments and still honor his legacy.

“You can look back on the Obama years as the glory days, but that doesn’t mean his record was perfect,” James said.

Adam Green, co-founder of the Progressive Change Campaign Committee, which supports U.S Senator Elizabeth Warren, said the push for more ambitious proposals should not be viewed as a shot at the former president.

“President Obama righted the ship in a better direction,” Green said. “Now we have an opportunity to move the ship much further and much faster toward progress.”