The CHP is California’s “State Police” since 1995: (i.e. “Texas Rangers” or “State Troopers”): https://www.chp.ca.gov/home/about-us/the-history-of-the-california-highway-patrol/milestones-in-time/merger-of-the-highway-patrol-and-the-state-police
And in 1990: “The CHP is directed by Governor Pete Wilson to provide law enforcement services to any city or police jurisdiction requesting assistance.”
I guess the Capitol Police could have just contacted the county sheriff or police dept. of the city where the guy lives. They probably figured CHP would “go along” better than a county sheriff.
If I were some big public figure and was receiving threats I thought were credible and I was told the California Highway Patrol would be investigating these cyber threats, I'd be thinking I was being pranked. Where's the hidden camera??...lol