Former President Barack Obama delivered a rebuke of President Trump and the Republican Party Friday, which was unusual, given his past reluctance to openly criticize Mr. Trump, or even mention him by name in public speeches. He said that the president capitalized on upheaval in the country and resentment, and reserved his harshest words for congressional Republicans, whom he said were "abdicating their responsibilities" when they failed to check the president. The speech, at the University of Illinois at Urbana-Champaign campus Friday, set his tone for campaigning ahead of the midterm elections.

The greatest threat to American democracy, the former president said, is not Donald Trump, Republicans in Congress, the Koch brothers, too much compromise from Democrats, or Russian hacking — the greatest threat to American democracy is cynicism that keeps Americans from participating in the democratic process, he said.

"As a fellow citizen, not as an ex-president but as a citizen, I'm here to deliver simple message and that is that you need to vote because our democracy depends on it," Obama said.

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"Just a glance at recent headlines should tell you that this moment really is different," he added. "The stakes really are higher. The consequences of any of us sitting on the sidelines are more dire."

Obama discussed key moments in American history — and the character that he believes made this nation strong. Ordinary people, Obama said, fought, marched and voted for equality, rather than being "bystanders" to history.

"That's the story of America," he said. "A story of progress."

But that progress, Obama noted, has not been a straight line — sometimes, it's two steps forward, one step back. And each time there is progress, someone incites backlash to stymie it, he said.

"Of course, there's always been another darker aspect to America's story," he said. "Progress doesn't just move in a straight line."

Obama said his successor is a "symptom," not the cause of the tribal divisions existing in today's political environment.

"It did not start with Donald Trump," Obama said. "He is a symptom, not the cause."

"He's just capitalizing on resentments that politicians have been fanning for years," Obama said, claiming Mr. Trump capitalized on a fear and anger that is rooted in the nation's past but also rooted in upheavals in the nation in recent years.

The president eviscerated congressional Republicans "maintaining some phony version of civility," responding with "vague statements of disappointment" when Mr. Trump "does something outrageous."

"That's not civility. That's abdicating your responsibilities," he said.

He also referred to anecdotes about hidden "resistance" depicted in a new Bob Woodward book about the Trump presidency and a New York Times anonymous op-ed.

"The claim that everything will turn out okay because there are people inside the White House who secretly aren't following the President's orders, that is not a check. I'm being serious here. That's not how our democracy's supposed to work. These people aren't elected. They're not accountable," he said.

"They're not doing us a service by actively promoting 90 percent of the crazy stuff that's coming out of this white house, and then saying, 'Don't worry, we're preventing the other 10 percent.' That's not how things are supposed to work. This is not normal," he said.

Obama is expected to hit the campaign trail running for Democrats this fall, as his party looks to take control of the House from Republicans hands. He's expected to hold a rally with Ohio gubernatorial candidate Richard Cordray Thursday, and with seven Democratic House candidates in California Saturday. The former president is also slated to campaign in Illinois and September later this month, and will headline a fundraiser for the National Democratic Redistricting Committee in New York City. Obama, who has already issued a list of 81 endorsements, is expected to issue a second round of them ahead of the midterms.

The Republican National Committee, responding to Obama's speech, said voters will reject Obama's strategy in 2018.

"In 2016, voters rejected President Obama's policies and his dismissiveness towards half the country. Doubling down on that strategy won't work in 2018 either," RNC spokesman Michael Ahrens said in a statement.

The former commander-in-chief made the case that today is a pivotal moment in history in which Americans need to push back against those who would encourage the worst in human nature and appeal to anger, fear and resentment. Obama, who received the Paul H. Douglas Award for Ethics in Government award for his service, lauded the importance of believing in principles of equality and decency over division.