The Illinois speech, in which Obama referred to the "state of our democracy", was created to deliver a message for Democrats for the coming midterm elections.
Obama's speech might help Trump.
But today, the former president made clear the consequences of being quiet -- of polite presidential deference - have become too "dire".
Mr Trump told supporters in Montana yesterday that Republicans needed to maintain control of Congress to stave off possible impeachment proceedings against him, although Democrats have played down any discussion of that approach.
It has always been a tradition of ex-presidents, following the example of George Washington, to leave office for a quiet retirement in the background of public life.
He said over the past few decades, the "politics of division and resentment and paranoia has found a home in the Republican party".
Trump also claimed, as he has in the past, that economic indicators were awful under Obama but excellent during his own presidency.
In fact, the previous POTUS went ahead and used Trump's name in the speech, something he's never done before after his time in the White House was over.
Texas woman takes off with baby after crashing car in chase
Losing control of the vehicle, she crashed into another auto , before grabbing the baby in a auto seat and trying to escape. It speeds across a grassy median and onto a slip road as the two left wheels appear to briefly lift off the ground.
"Let's just remember when this economy started" improving, he said. "He is a symptom, not the cause", Obama said of Trump as a round of applause broke out.
"The claim that everything will turn out OK because there are people inside the White House who secretly aren't following the president's orders, that is not a check", Obama said.
Obama's campaign activity will continue through October and will include fundraising appearances, according to an Obama adviser. On Twitter, Shapiro posted, "Obama lecturing us is LITERALLY how you got Trump".
"We're supposed to stand up to discrimination", he said.
The result is a strategy of big events in blue corners of the country, quiet fundraisers with donors and a series of digital videos or robo-calls, meant to drive Democratic attention and turnout in a targeted way. He's expected to hold a rally with OH gubernatorial candidate Richard Cordray Thursday, and with seven Democratic House candidates in California Saturday.
Obama is also planning campaign trips to Pennsylvania in September, an Obama official said, as well as a NY fundraiser for the National Democratic Redistricting Committee, an organization led by former Attorney General Eric Holder, Obama's longtime friend. "People in power want us to believe that the rest of us are powerless to solve our problems through democracy".
I would not be surprised if Obama - as long as he is in IL - does some campaigning with Democratic governor nominee J.B. Pritzker.
"You've got to do more than retweet a hashtag, you've got to vote", he said.