US President Barack Obama and first lady Michelle Obama arrive to board Air Force One for travel to Chicago to deliver a farewell address, from Joint Base Andrews, Maryland, US, January 10, 2017. [Photo/Agencies]

CHICAGO - President Barack Obama will give a farewell speech to the nation on Tuesday, looking back at his legacy as he encourages supporters demoralized by the election of Republican Donald Trump to feel optimism about the future of the country.

The Democratic president is feeling some nostalgia as he prepares to leave the White House on Jan 20 after eight years in office. His top policy achievements were jolted by the Nov 8 election of Trump, who has threatened to undo Obama's actions on issues ranging from advancing healthcare reform to curbing climate change.

In an 8 pm CST (0200 GMT Wednesday) speech at McCormick Place, the city's main convention center, Obama will talk about how his experience in Chicago - at the start of his political career - taught him that change happens from the grassroots.

"I first came to Chicago when I was in my early twenties, still trying to figure out who I was; still searching for a purpose to my life," Obama was set to say, according to excerpts released by the White House.

"It was in neighborhoods not far from here where I began working with church groups in the shadows of closed steel mills.

It was on these streets where I witnessed the power of faith, and the quiet dignity of working people in the face of struggle and loss."

First lady Michelle Obama, Vice President Joe Biden, his wife, Jill Biden, and many current and former White House staff members and campaign workers were expected to attend the speech.

"The president is not one to be overly sentimental, but given the circumstances, I think it would be unrealistic to expect anybody to not feel some nostalgia for this moment," his spokesman, Josh Earnest told reporters traveling with Obama.

Even the final trip on the presidential aircraft was a moment tinged with wistfulness. It was Obama's 445th trip on the presidential aircraft, a perk he has said he will miss when he leaves office. All told, he will have spent more than 2,800 hours or 116 days on the plane during his presidency, Earnest said.

Obama has said he plans to reflect on his administration's achievements in his address, encouraging supporters to keep fighting for issues like the environment, gay rights and economic equality.

Obama plans to remain in Washington for the next two years while his younger daughter, Sasha, finishes high school. He has indicated he wants to give Trump the same space that his predecessor, Republican President George W. Bush, gave Obama after leaving office by not maintaining a high public profile.