Harris has issued a statement on the fatal shooting of Sonya Massey, an unarmed Black woman who was shot in her own home by a deputy after calling 911 to report a possible intruder.

"Sonya Massey deserved to be safe," Harris wrote in the statement. "After she called the police for help, she was tragically killed in her own home at the hands of a responding officer sworn to protect and serve. Doug and I send strength and prayers to Sonya’s family and friends, and we join them in grieving her senseless death."

Police body camera footage was released by by the Illinois State Police Monday afternoon.

"The disturbing footage released yesterday confirms what we know from the lived experiences of so many – we have much work to do to ensure that our justice system fully lives up to its name," Harris said.

Harris said he joined Biden in calling on Congress to pass the George Floyd Justice in Policing Act -- a bill she coauthored when she served in the Senate.

"In this moment, in honor of Sonya’s memory and the memory of so many more whose names we may never know, we must come together to achieve meaningful reforms that advance the safety of all communities," Harris said.

-ABC News' Sarah Beth Hensley

While the vetting process is just getting started, a senior administration official told ABC News' Martha Raddatz that Pennsylvania Gov. Josh Shapiro and Arizona Sen. Mark Kelly are the leading candidates to be Harris' running mate.

The two men come from key 2024 battleground states, and have experience trouncing Trump-endorsed candidates.

Shapiro, 51, was Pennsylvania's attorney general before being elected governor in 2022 after defeating Republican Doug Mastriano.

Kelly, a 60-year-old former astronaut and Navy captain who is married to former congresswoman Gabby Giffords, won his Senate seat in 2022. He defeated Republican challenger Blake Masters.

Actor and Democratic megadonor George Clooney, whose op-ed in the New York Times calling on Biden to step aside ignited a political firestorm, told CNN he is committed to supporting Vice President Harris.

"President Biden has shown what true leadership is. He's saving democracy once again. We're all so excited to do whatever we can to support Vice President Harris in her historic quest," he said in a statement first provided to the network.

Vice President Kamala Harris will on Tuesday hold her first presidential campaign rally in Milwaukee, Wisconsin, according to her campaign.

The Harris campaign signaled in a memo that the vice president would take on former President Donald Trump and his running mate, Sen. JD Vance, on abortion and Project 2025.

The campaign said Harris "is prepared to prosecute the case against Donald Trump -- and there’s no better place to drive this contrast than Milwaukee, Wisconsin."

The rally comes days after Republicans held their nominating convention in Milwaukee, and weeks before the Democrats hold their convention in Chicago.

"Vice President Harris’s visit will highlight the choice facing Wisconsinites: between Donald Trump, the convicted felon who would drag this country backwards, and her brighter vision for the future, where our freedoms are protected and every American has a fair shot," the campaign said in the memo.

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