Obama's speech in the university's 1,300-person auditorium has seen sizable interest from the school's student body, according to university spokesman Jon Davis, who said they had received around 22,000 requests for tickets.
"They're undermining our alliances, cozying up to Russian Federation", he said.
"You, Barack, you elected Donald Trump".
Through his extraordinary speech, which was full of an unusual number of criticisms from a former president, Obama also layered in his quintessential hope and calls for unity.
Lamenting the current political climate, Obama said that Trump was a "symptom, not a cause".
"You happen to be coming of age during one of those moments", Obama said.
Trump brought up the former president's speech again while he was dancing on the grave of Obamacare's individual mandate, which Republicans eliminated in their tax bill. The remarks amounted to a stinging indictment of political life in the Trump era.
"Appealing to tribe, appealing to fear, pitting one group against another, telling people that order and security will be restored if it weren't for those who don't look like us or don't sound like us or don't pray like we do - that's an old playbook", he said.
Still, he believes America will make it through this period: "We have been through much darker times than these and somehow each generation of Americans have carried us through to the other side". "It's indifference. It's us not doing what we're supposed to do". "And we're sure as heck supposed to stand up clearly and unequivocally to Nazi sympathizers".
He specifically called out Mr Trump's response to the violence in Charlotesville, Virginia in 2017, asking the crowd: "How hard can that be, saying that Nazis are bad?"More news: Rapper Mac Miller dead at 26 after long substance struggle
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The president was widely censured by officials from across the political spectrum, and later clarified that he condemned neo-Nazis and white supremacy.
The speech was "something different", said Esther Castaneda, 34, a small business owner from Orange, California.
Obama says during a speech Friday at the University of IL that Trump is capitalizing on the same resentments, fear and anger that politicians have fanned for years.
Just a day earlier, Obama had criticised the President for his relationship with Russian President Vladmir Putin and for failing to condemn white supremacists previous year in Charlottesville.
"It's supposed to be the party... of fiscal conservatism". After a particularly brutal loss in the 2010 midterms - 63 House seats and six Senate seats - Obama said the party had received a "shellacking". In one of the speech's more timely soundbites, Obama blasted his successor's fierce and frequent attacks on the press.
Obama is re-entering the public eye two months before voters head to the polls for the midterm elections on November 6.
"You didn't go out to vote". "You can not sit back and wait for a savior".
"You need to vote because our democracy depends on it". More than six in 10 respondents to a Gallup poll released in February said they approved of the way Obama handled the job.
"I watched it, but I fell asleep", Trump claimed.