The first night of the DNC is underway in Chicago, with the convention officially called to order.

Tonight's theme is "For the people" and the evening is being hosted by actor Tony Goldwyn -- who famously played a president on TV in the ABC series "Scandal."

Four people were arrested after several protesters broke through an outer security fence outside the United Center during the pro-Palestinian rally "March on the DNC," police said.

There is a heavy police presence outside the venue, where the DNC will soon kick off.

The inner perimeter fence was not breached, police said.

President Joe Biden posted a video on social media touting his accomplishments and prominently features Vice President Kamala Harris just ahead of his speech at the DNC on Monday evening.

"Thank you, America, for keeping the faith," Biden wrote in a post on X.

Throughout the video, images of Harris flash on the screen, including of her meeting with Parkland shooting victims' parents, meeting with world leaders and sharing a moment with Justice Ketanji Brown Jackson.

-ABC News' Fritz Farrow, Gabriella Abdul-Hakim and Will McDuffie

Greetings from the Windy City -- or, as Chicago should be called, the City of Conventions. Chicago has hosted more political conventions than any other city in America. Before the 26th major-party political convention in Chicago history kicks off, watch this video my colleagues and I made this morning to familiarize yourself with the history of the other 25.

-538's Nathaniel Rakich