A few short weeks ago, Joe Biden was set to headline the Democratic National Convention — but after a brutal political comedown, he's now the warm-up act for Kamala Harris.

For a proud man like the 81-year-old U.S. president, his speech on the first day of the party's gathering in Chicago on Monday is sure to come with conflicting emotions.

Still harboring frustration over his exit from the White House race, Biden will be trying to balance his feelings with the need to help his vice president beat Republican Donald Trump in November.