"These are extraordinary times. Dangerous times," Obama warned in an extraordinary indictment of the behavior of a successor to whom he handed power in January 2017 and who has torn at the conventions that restrain presidents ever since.

It was a revealing moment in an enthralling clash of philosophy, temperament and style that unfolded Friday between a current and former president who epitomize opposing currents in an epochal political moment and are now in direct conflict ahead of the midterm elections.

The campaign trail face-off between Obama and Trump also capped a consequential week that saw the awakening of the Washington establishment after John McCain's funeral turned into an indictment of Trumpism and in which Trump battled an enemy within his own administration.

Obama, ditching his self-imposed political exile, warned of a moment of unique national peril, in which demagogic forces -- aka Trump -- are undermining the structures of democratic government to build their own omnipotence.

"They start undermining norms that ensure accountability and try to change the rules to entrench their own power," Obama said in a major speech in Illinois.

"It shouldn't be Democratic or Republican to say that we don't pressure the attorney general or FBI to use the criminal justice system as a cudgel to punish our political opponents -- or to protect members of our own party from prosecution just because an election's coming up," he said.

At almost the same moment, aboard Air Force One, the current President told reporters he wanted Attorney General Jeff Sessions to hunt a senior official within his administration who sent the White House reeling with a devastating anonymous New York Times op-ed that branded him unfit for power.

"Here's criticism where you can't fight back. 'Cause you have somebody doing it anonymously," Trump said, after he effectively ordered the criminal investigative functions of the state to purge an opponent who has not committed a crime but has merely exercised a First Amendment right.

It was far from the first time Trump has appeared to shun conventions designed to shield the instruments of justice from political interference. He has spent months lambasting the FBI and the Justice Department over the Russia investigation. Earlier this week he complained that Sessions should not have allowed two Republicans to be indicted over corruption allegations.

Friday's competing appearances were the latest intense intersection of two giant, idiosyncratic political opposites who are again waging a struggle for the political soul of their nation.

Ever since Trump made the birtherism conspiracy his bridge to politics from the tabloid life of a tycoon and real estate star, he and Obama have been locked in a mutually antagonistic embrace , as opposites in decorum and ideology.

That mirror image was on show Friday.

Opposing styles

Obama, serene and intellectual, chose the conventional medium for a politician, a long, reasoned, multi-layered speech, to frame a political problem -- the conditions that led to the rise of Trump -- and to give Democrats a battle plan to restore America's ailing democracy.

He bemoaned missing checks and balances in Washington, the indifference of Republicans to Trump's power grabs, the predominance of bullies, and walls being put up around America, and he diagnosed a "backlash from people who are genuinely, if wrongly, fearful of change."

In signature style, he called on young people to vote, campaign and fight for their democracy, and argued that despite everything there is a unifying American "common ground."

At times, he appeared to be renewing his own faith in a brand of politics that shot him to power from nowhere in 2008 but whose effectiveness has been called into question -- even by some more radical Democrats -- as Trump crushes his legacy and the GOP monopolizes power.

Trump, the king of the barbed tweet, who reinvented the way to win the White House, brawled on social media, sparred with reporters and in a stream-of-consciousness campaign speech of his own displayed his more gritty, authoritarian and aggressive political methodology

He mocked Obama's approach. "I watched it, but I fell asleep. I've found he's very good for sleeping," Trump said in Fargo, North Dakota, before reeling off a list of his administration's achievements and slamming America's foreign trade partners.

"I don't want to be taken advantage of by other countries in the world," he said.

The thrust of Obama's argument was that America is a great nation that has slumped into crisis because its core values are being trampled. Trump's -- in line with his strongman's instincts -- was that he inherited a humbled and disrespected country and he had already redeemed it.

He told his crowd that a strapping man had come up to him at his event with tears rolling from his eyes and said: "I want to thank you, Mr. President, for saving our country."

Same aim

JUST WATCHED Trump: I fell asleep during Obama speech Replay More Videos ... MUST WATCH Trump: I fell asleep during Obama speech 01:32

In essence, Trump and Obama were trying to do the same thing -- electrify grass-roots voters and drive turnout in midterm elections that both view as the most crucial for decades and that will be crucial to the fate of the Trump presidency.

Obama is a singular political figure. While he won two impressive general election victories, he found it more difficult to bestow his appeal to Democrats in midterm elections, when he was not on the ballot. It may be even more difficult to do so when he is out of power.

Trump is also unique, and it is not clear whether he will be any more successful in transferring his magnetic appeal with the grass roots to Republican candidates in midterm polls.

Obama found out how a presidency can be crippled by the loss of the House of Representatives. Unless Trump can buck history, he may experience an even more painful defeat, given the multiple political and legal storms already battering his White House.

Their combat on Friday opened up intriguing new possibilities for the fall campaign, and risks for both.

Obama had stayed out of the spotlight for the last 19 months for a reason, apart from honoring the tradition that presidents don't usually criticize their predecessors. He knows that he has now given Trump the political target he has often lacked during his presidency.

Obama, who is reviled by many Trump voters, could become an organizing catalyst for grass-roots Republicans as well as Democrats.

The more President @BarackObama speaks about the 'good ole years' of his presidency, the more likely President @realDonaldTrump is to get re-elected.



In fact, the best explanation of President Trump's victory are the "results" of the Obama Presidency! — Lindsey Graham (@LindseyGrahamSC) September 7, 2018

South Carolina Sen. Lindsey Graham spotted the opening for Republicans and for Trump in 2020, by tweeting: "The more President @BarackObama speaks about the 'good ole years' of his presidency, the more likely President @realDonaldTrump is to get re-elected."

On the other hand, many Democrats and others who remember Obama's presidency and conduct in the White House fondly have often wondered why he has not been more vocal in taking on Trump. There is still no Democrat with the capacity to frame a political problem, distill a message and deliver it as well as Obama.

Still, his re-emergence was not universally welcomed by serving Democratic lawmakers.

Delaware Sen. Chris Coons told CNN's Wolf Blitzer he was worried that the midterms could become fixated on personalities rather than the needs and concerns of voters.

"We have got a President who is really adept about making the day about him, day in and day out. My concern here is President Obama may be simply feeding that dynamic where it is all about President Trump," he said.

But one thing is clear: With Obama and Trump going at it, the fall campaign just got a lot more interesting.