Former US President Barack Obama on Friday gave an impassioned speech in which he railed against President Donald Trump and the Republican Party for abandoning the party's core principles and harming American democracy.

Obama warned, however, not to solely blame Trump for the rise of the far right and white nationalism, saying that Trump was a "symptom, not the cause" of the nation's divisive politics.

The former leader spoke to a packed auditorium at the University of Illinois. The speech marked the beginning of what will be a busy next few months for Obama as he travels from state to state campaigning for various Democrats in the run-up to the midterm elections in November.

'What happened to the Republican Party?'

"What happened to the Republican Party?" Obama asked. "They're undermining our alliances, cozying up to Russia…[their] central organizing principle in foreign policy was the fight against communism and now they're cozying up to the former head of the KGB."

He also noted that "the politics of division and resentment and paranoia has unfortunately found a home in the Republican Party."

In an uncharacteristic move, Obama named Trump directly, accusing him of "capitalizing on resentments that politicians have been fanning for years." Typically, former US presidents refrain from directly criticizing their successors.

Obama further criticized the government's sweeping tax reform policy, asking why the party "of fiscal conservatism" would add so much to the national deficit.

The ex-president urged young people to go out and vote and engage with the issues that mattered to them, saying "you cannot sit back and wait for a savior." He also called for a return to "honesty and decency" in government.

"Don't get anxious. Don't retreat. Don't binge on whatever it is you're binging on. Don't lose yourself in ironic detachment. Don't put your head in the sand."

es/msh (AP, AFP)