Barack Obama has launched an unprecedented attack on Donald Trump's presidency as he returned to the political spotlight for the first time since leaving the White House.

As he returned to the political spotlight ahead of November's midterm elections, the former US president accused Mr Trump of "cosying up" to Vladimir Putin and adopting the "politics of fear and resentment".

In a speech which lasted more than an hour, Mr Obama delivered a series of attacks against Mr Trump's policies since entering office, from tax cuts for the "wealthiest Americans" to repealing climate change legislation.

Charlottesville

Mr Obama rebuked Mr Trump's response to a violent white supremacist rally in Charlottesville, Virginia last year, asking a crowd at the University of Ilinois: "How hard can that be, saying that Nazis are bad?"

Mr Trump said there were some "very fine" people on both sides of the protests, in which neo-Nazis clashed with anti-racism demonstrators leaving one woman dead and several injured.

Mr Trump claimed the "alt-left" bore some responsibility for the violence and refused to condemn the "alt-right" activists.

View photos Barack Obama delivered a sharp rebuke to Donald Trump's presidency Credit: Reuters More

In a reference to the incident on Friday, Mr Obama told the audience: "We're supposed to stand up to discrimination. And we're sure as heck supposed to stand up, clearly and unequivocally, to Nazi sympathizers. How hard can that be, saying that Nazis are bad?"

Economy

Mr Obama also poked fun on the issue the current president frequently heralds as one of his greatest achievements - the strong economy.

Mr Obama was eager to "remind" voters that the economic recovery - one of Mr Trump's favourite talking points - actually began "in 2015" under his presidency.

"When you hear how great the economy's doing right now, let's just remember when this recovery started," he said.

The Republican party

Mr Obama also hit out at the current face of the Republican Party, calling it a "radical" organisation which has embraced conspiracy theories, attacked voting rights and rejected climate change.

He said: "What happened to the Republican party? Its central organising principle in foreign policy was the fight against communism and now they're cosying up to the former head of the KGB, actively blocking legislation that would defend our elections from Russian attack. What happened?"

He went on to attack the administration's repeal of climate change legislation, saying: "They've made it so that the only nation on earth to pull out of the global climate agreement, it's not North Korea, it's not Syria, it's not Russia or Saudi Arabia. It's us. The only country."

Pressuring aides

Mr Obama was especially stern in his condemnation of Mr Trump's pattern of pressuring law enforcement officials, including Attorney General Jeff Sessions.

Mr Trump has repeatedly called on Mr Sessions to fire special counsel Robert Mueller and earlier this week blamed the Justice Department for charging two incumbent Republican members of Congress, arguing the moves could jeopardise their seats ahead of the election.

"It should not be a partisan issue to say that we do not pressure the attorney general or the FBI to use the criminal justice system as a cudgel to punish our political opponents," Mr Obama said. "Or to explicitly call on the attorney general to protect members of our own party from prosecution because an election happens to be coming up. I'm not making that up. that's not hypothetical."

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