Chicago, Illinois - Former President Barack Obama lashed out at President Donald Trump for conducting an "assault on our democratic institutions" as he paid tribute to the late civil rights activist Jesse Jackson on Friday.

Obama joined former Presidents Joe Biden and Bill Clinton to mark the life of Jackson after his death at age 84.

"Each day we wake up to some new assault on our democratic institutions, another setback to the idea of the rule of law, an offense to common decency," Obama said after receiving a rapturous welcome at the event in Chicago.

"Every day, you wake up to things you just didn't think were possible.

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"It may be tempting to get discouraged, to give into cynicism... [but] this man, Reverend Jesse Lewis Jackson, inspires us to take a harder path."

Ahead of the speeches, a choir sang as attendees photographed a large panel emblazoned with one of Jackson's mantras, "keep hope alive."

A blue-lit image of Jackson was projected on a giant screen behind an altar.

Jackson, who died on February 17, was a close associate of Martin Luther King Jr. in the 1960s and remained a prominent voice of African Americans on the national stage for more than six decades.