Barack Obama warned Democrats against being “complacent or smug” about the presidential race at a grassroots fundraiser on Tuesday for presumptive Democratic nominee Joe Biden.

The former president called on viewers to learn the lessons from 2016 and not take the election for granted.

Referencing what he called a “great awakening” among younger Americans pushing for reforms, Mr Obama said that “just because this energy is out there does not mean that it assures our victory and it does not mean that it gets channelled in a way that results in real change”.

“There’s a backlash, that is fierce, against change,” he said.

Mr Obama referenced the division among Americans that he said President Donald Trump “exploits”, as well as new challenges to voting rights in recent years.

“We can’t be complacent or smug or suggest that somehow it’s so obvious that this president hasn’t done a good job because, look, he won once, and it’s not like we didn’t have a good clue as to how he was going to operate the last time,” Mr Obama said.

He implored the audience to be engaged with Mr Biden’s presidential campaign, declaring that “whatever you’ve done so far is not enough”.

The fundraiser marked Mr Obama’s official return to the presidential campaign trail and underscored his unmatched popularity within the Democratic Party.

Mr Biden, who appeared virtually alongside Mr Obama at the event, said it raised a record-breaking 7.6 million dollars (£6.06 million) from more than 175,000 individual donors.

Mr Trump’s Dallas fundraiser earlier this month raised more than 10 million dollars (£7.98 million).

Tuesday’s event was a kickoff of what Mr Obama’s team say will likely be a busy schedule heading into the autumn, as he looks to help elect not just Mr Biden but Democrats running for the House of Representatives and the Senate.

And his comments suggest Democrats are taking very seriously the possibility that their base could grow too comfortable this autumn, with a number of state and nationwide surveys showing Mr Biden with significant, often double-digit leads over Mr Trump.

Mr Obama sometimes struggled to lift other Democratic candidates while he was in the White House, notably losing control of the House in 2010 and the Senate in 2014.

But in the era of President Donald Trump, Democrats believe Mr Obama’s appeal, especially among black and younger voters, can help boost energy for Mr Biden.

Democrats hope widespread disenchantment with President Donald Trump will bring out more of the party’s voters for the November election Credit: Ross Franklin/AP

“There’s two groups of voters that Biden needs to move,” said Dan Pfeiffer, former White House communications director.

“You have the four million Obama 2012 voters that sat out in ’16, Obama obviously has cache with them. And you have to persuade some number of voters who voted for Barack Obama in 2012 and either Trump or a third party candidate in 2016, and Obama obviously is very, very high-performing with those as well.”

Indeed, during Tuesday night’s fundraiser, Mr Obama made a frequent pitch directly to young voters, telling them he was “hopeful” about the new energy for reform he had seen in the younger generation but warning them not to get discouraged with a political process he said “is always going to be slower” and “less satisfactory” than engaging with a social movement through public demonstrations.

Mr Obama endorsed Mr Biden with a video message in April but kept an otherwise low profile throughout the primary and largely avoided wading into national politics.

In recent weeks, however, he has reemerged publicly to speak out on policing and the civil unrest that followed the police killing of George Floyd in Minneapolis.

Some Democrats say that, in the wake of Mr Floyd’s killing, Mr Obama’s voice as an advocate for Mr Biden and a leader for the party is needed.

Given what’s going on with criminal justice reform and Black Lives Matter, having the first African American president out there publicly backing Biden is extremely helpful

Former Bernie Sanders adviser Ben Tulchin

“Biden doesn’t have the strongest record on criminal justice reform so having Obama there is helpful in reinforcing that issue,” said Ben Tulchin, who polled for progressive Vermont senator Bernie Sanders’ presidential campaign.

“Given what’s going on with criminal justice reform and Black Lives Matter, having the first African American president out there publicly backing Biden is extremely helpful.”

But Obama’s reemergence is not without risks for Biden.

For Trump’s campaign, it offers an opportunity to resurface some of their favorite political attacks — charges that the Obama administration’s policies undermined the American middle class and U.S. interests abroad.

They believe the focus on Obama will help reinvigorate Trump’s base, and remind waffling Trump voters — those considering voting for Biden, or staying home — of their dissatisfaction with the prior administration.

And they see a potential opportunity to drive a wedge between Biden and his base by resurfacing issues from the Obama administration — like the high rate of deportations — that riled progressives during the Democratic primary.