Barack Obama re-entered the political arena today, declaring himself a "fellow citizen" rather than former president.

Why it matters: The most successful Democratic politician of his generation is breaking with precedents from a more civil era. It's highly unusual for a former president to criticize a current one in such blunt terms.

In a fiery speech at the University of Illinois, Obama directly criticized President Trump, linking him to a "darker aspect" of the American story.

"Each time we painstakingly pull ourselves closer to our founding ideals ... somebody somewhere has pushed back. The status quo pushes back."

to our founding ideals ... somebody somewhere has pushed back. The status quo pushes back." "It did not start with Donald Trump. He is a symptom, not the cause."

He is a symptom, not the cause." "He's just capitalizing on resentments that politicians have been fanning for years."

The big picture: Obama's message to America is that Trump isn't normal, and shouldn't be accepted as normal.

"[W]e do not pressure the Attorney General or the FBI to use the criminal justice system as a cudgel to punish our political opponents."

to use the criminal justice system as a cudgel to punish our political opponents." "Or to explicitly call on the Attorney General to protect members of our own party from prosecution because an election happens to be coming up."

of our own party from prosecution because an election happens to be coming up." "[W]e don't threaten the freedom of the press... because they say things or publish stories we don't like.

because they say things or publish stories we don't like. "[Y]ou never heard me threaten to shut [Fox News] down , or call them enemies of the people."

, or call them enemies of the people." "And we're sure as heck supposed to stand up ... to Nazi sympathizers.

... to Nazi sympathizers. "How hard can that be? Saying that Nazis are bad."

Between the lines: Obama didn't forget Republicans in Congress:

"Republicans who know better in Congress ... are still bending over backwards to shield this behavior from scrutiny or accountability or consequence."

backwards to shield this behavior from scrutiny or accountability or consequence." "None of this is conservative... It sure isn't normal. It's radical."

Trump's response to Obama's speech, per the AP: "I’m sorry, I watched it, but I fell asleep... I found he’s very good for sleeping.”

The bottom line: Buckle up. This is just the beginning for Obama.