"It's not for sale".
Obama continued: "And when people don't participate, then that vacuum is filled by lobbyists and special interests and we get into a downward spiral where people get more and more discouraged and they think nothing's going to make a difference". To all the young people who are here today, there are now more eligible voters in your generation than in any other, which means your generation now has more power than anybody to change things.
"In the end, the threat to our democracy doesn't just come from Donald Trump or the current batch of Republicans in Congress or the Koch Brothers and their lobbyists, or too much compromise from Democrats, or Russian hacking".
Former Obama communications director Dan Pfeiffer said on CNN that Obama can effectively reach voters in parts of the country he won in 2012, but which voted for Trump in 2016.
The "good news" Obama said is "in two months we have a chance to restore some sanity in our politics".
He criticized Republican efforts to curb or remove laws involving voting rights, campaign finance limits and the social safety net while backing tax cuts and embracing "wild conspiracy theories", including one once endorsed by Trump - that Obama was not born in the U.S.
"It's apathy", he said. And we sure as heck are supposed to stand up clearly and unequivocally to Nazi sympathizers.
In that speech Friday at the University of IL at Urbana-Champaign, Obama took direct aim at Trump, referring to "crazy stuff that is coming out of this White House".
Obama spoke to a packed auditorium with an audience of about 1,100 students, faculty and community members.
The former president explained he planned on following the precedent set by George Washington "to gracefully exit" the political stage, but speaks now as a citizen.
Trump, speaking at a rally later that day, said Obama was trying to take credit for a strong economy. "He's just capitalising on resentments that politicians have been fanning for years, a fear and anger that's rooted in our past but it's also born out of the enormous upheavals that have taken place in your brief lifetimes".
"I'm sorry, I watched it, but I fell asleep".
Meanwhile, Michelle Obama is also stepping up her political involvement ahead of the November midterm election.
Obama's re-emergence comes as both parties are girding for a November election widely seen as a referendum on Trump.
Obama will hit the campaign trail on Saturday to back Democrats in key races. Each of the seven candidates that Obama campaigned for on Saturday fit that description.
But Obama pointed to his own role in bringing the US out of one of the worst economic recessions it has experienced, saying "let's just remember when this recovery started". Further the Democratic former president assailed Republicans as "unwilling to find the backbone" to challenge Trump head-on accusing them instead of answering "outrageous" actions with "vague statements of disappointment".