What's happening on the campaign trail todayVice President Kamala Harris today picked Minnesota Gov. Tim Walz as her running mate. He joined her onstage at this evening's rally in Philadelphia, where they're kicking off a swing through battleground states.Walz has been governor since 2019 and previously represented Minnesota's 1st Congressional District in the U.S. House for over a decade. Before his political career, he taught high school, coached football and served in the Army National Guard for 24 years.Where there's Harris, there's also Sen. JD Vance of Ohio. Former President Donald Trump's running mate held a rally in Philadelphia hours before Harris took the stage at her event. Vance then plans to rally supporters in the same cities Harris and Walz are visiting this week.It's primary day in Kansas, Michigan, Missouri and Washington. Some of the big contests include challenges for Democratic Rep. Cori Bush of Missouri, who's a member of the "squad," and Rep. Dan Newhouse of Washington, a Republican who voted to impeach Trump.