Speaking to a largely young audience at the University of IL at Urbana-Champaign, Obama urged them to vote if they wanted to make a difference - "In two months we have the chance, not the certainty but the chance, to restore some semblance of sanity to our politics".
Obama aides tell CNN that his message on Saturday will be similar to the lengthy and direct indictment he delivered on Friday in IL, where the former President reentered the political fray by attacking Trump, slamming him for "capitalizing on resentment that politicians have been fanning for years".
Obama, in making his first political speech with the midterms in mind, implored people to vote. "I have to say this to President Obama: if Democrats got in, with their agenda, in November of nearly two years ago, instead of having 4.2 up, I believe you would have 4.2 down - you'd be in negative numbers".
"Just a glance at recent headlines should tell you this moment really is different", he said.
He also nodded to modern progressive policies by saying that "we need more women in charge" in America.
The former president's remarks in IL came ahead of a series of campaign stops to help fellow Democrats running in the November midterm elections.
The president - who was traveling in North Dakota - took a swipe back at his predecessor after the speech, telling a crowd of supporters at a fundraiser: "I watched it, but I fell asleep".
But, Mr Obama added, when there is a vacuum in democracy, "other voices fill the void".
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Obama had so far been reluctant to publicly criticize his successor, although last week he appeared to chide Trump, without naming him, in a eulogy for the late Republican Senator John McCain. "It's radical. It's a vision that says our protection of our power is all that matters", Obama said.
"I found he's very good for sleeping."
"There are people out there right now that are counting on us to make sure they still have health care after this election", Obama said.
"We're supposed to stand up to bullies", Obama said.
Obama's speech might help Trump.
Obama will hit the campaign trail on Saturday to back Democrats in key races. How hard can it be to say that Nazis are bad?'
In a wide-ranging speech punctuated by frequent applause, Obama criticized the divisive politics of the era, decrying Trump's attacks on the media and the judiciary, his eagerness to work with Russian Federation while neglecting traditional alliances.
The event, organized by the Democratic Congressional Campaign Committee, was an attempt to boost seven Democrats running in districts Hillary Clinton won in 2016 but which are represented by the Republicans in the House.