Former President Obama on Friday delivered a blistering criticism of the political tactics of his successor President Trump, saying he had built on the fears of the powerful as they look to diminishing importance in a rapidly changing nation.

Former President Barack Obama speaks to a full crowd at the University of Illinois campus in Urbana on Friday. Stephen Haas/The News-Gazette via Associated Press

“It did not start with Donald Trump,” Obama said during a noon speech at the University of Illinois Urbana-Champaign. “He is a symptom not the cause. He’s just capitalizing on resentments that politicians have been fanning for years, the fear and anger that’s rooted in our past.”

The former president said both parties had, at times, been “infected” with the kind of politics he said the nation should abhore. He praised Republicans who in the past had helped expand civil rights and other protections and said neither party “has had a monopoly on wisdom.”

But he fiercely repudiated the brand of Republicanism being practiced in the Trump era, citing the White House and Congress’ refusal to punish Russia harshly for interfering in the 2016 election, and of rapidly expanding the federal deficit.

He noted the rush to approve Supreme Court justices nominated by President Trump – after Capitol Hill Republicans refused for 10 months to consider his nominee, Merrick Garland.

He drew attention as well to the current president’s attempt to, as he put it, use the Justice Department as a “cudgel” against political opponents.

“None of this is conservative,” he said. “It’s not conservative. It sure isn’t normal. It’s radical. It’s a vision that says the protection of our power and those who back us is all that matters.”

Going further than he has in the past, Obama called the current political environment “extraordinary.”

“These are extraordinary times, and they are dangerous times,” he said.

“Here’s the good news – in two months we have the chance … to restore some semblance of sanity to our politics.”

Obama also defended his own administration from near-constant criticism by Trump, noting its capture and killing of Osama bin Laden and its handling of the economic collapse of 2008.

“Let’s just remember when this economy started” improving, he said.

The address comes as the former president and first lady delicately re-enter the political fray ahead of the midterm elections, a move filled with peril and opportunity as the most powerful duo in Democratic politics test whether they can help handicap Trump’s presidency without also motivating his supporters to the polls.

Trump has consistently used Obama as a foil on Twitter to energize his voters, while Democratic incumbent senators are struggling for reelection in states where Obama has never been particularly popular. Republicans also continue to use Obama’s image in campaign ads, like a special House election in Pennsylvania and the West Virginia Senate contest, where the Republican candidate, Patrick Morrisey, often boasts of his efforts to stop Obama policies with lawsuits.

To avoid such traps, Obama in his post-presidency has chosen his spots carefully, opting to do targeted robo-calls last year to support Democratic Sen. Doug Jones’s upset victory in Alabama instead of a more high-profile public appearances. He has also hewed thus far to high-minded rhetoric that contrasts starkly with Trump’s brawling approach to politics. Obama denounced the “politics of fear and resentment” in a summer address in South Africa and in a recent eulogy for Sen. John McCain, R-Ariz., he seemed to take a swipe at Trump, without naming him, when he described “politics that pretends to be brave and tough, but in fact is born of fear.”

“I’m asking you to be neither blind to, nor dismayed by, reality – but motivated by it,” Obama wrote in an email Thursday to supporters of Organizing for America, a grass roots organization he founded. “Those who believe in democracy and civil rights and a common humanity will always have the upper hand.”

The cautious approach points to a delicate balance Obama is trying to strike. He aims to criticize Trump without giving up his own post-partisan stature as a president emeritus, which he has publicly embraced in a series of events with former Republican President George W. Bush. And he is wary of outshining the next generation of liberal leaders, whose success he has described as the greatest ambition of his post-presidency.

“He is acutely aware that he has a mixed record of success when his name is not on the ballot,” said one person familiar with President Obama’s thinking, who asked not to be named discussing internal deliberations. “We understand that we energize the other side like very few people do, so we have to be thoughtful about where we campaign.”

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. A top focus of his efforts will be helping Democrats retake the House, which he will kick off on Saturday with a Democratic Congressional Campaign Committee rally in Orange County, California, for the seven Democrats running there in Republican-held districts Hillary Clinton won in 2016.

He has also made a priority of helping individual candidates ingovernors’ and state legislative races by working closely with former Attorney General Eric Holder, who has founded a group, the National Democratic Redistricting Committee, which is focused on expanding Democratic state power in advance of the next round of congressional gerrymandering. Of the 81 candidates Obama endorsed in August, 40 were running for state legislative seats.

“There is no one else in the Democratic Party that is able to focus people’s attention on an issue the way that he can,” said Patrick Rodenbush, the communications director for the Holder group, for which Obama recently sat to shoot a promotional video.

He will appear at a Sept. 13 rally in Ohio with Richard Cordray, a former Obama appointee, who is running for governor in a state that is also one of the top targets for the Holder effort. Further campaign stops will be announced later in the fall.

Organizing for America, meanwhile, has launched a parallel effort focused largely on House and state legislative races. The group has trained 200 team leaders around the country, many of whom are focused on training groups that can volunteer for House campaigns.

Michelle Obama has opted to avoid, for now at least, any explicit candidate advocacy, choosing to throw her lot in with another new group, When We All Vote, that has been gathering celebrity endorsers in an effort to launch a major voter registration drive later this month. Other co-chairs of the project include the actor Tom Hanks and musicians Janelle Monáe, Faith Hill and Tim McGraw.

“I want every single one of you to host events in your community to get registered and to get them fired up,” she said in a conference call with organizers Wednesday, when she announced events she would attend later this month in Las Vegas and Miami.