On July 26, the Public Policy Institute of California released a poll for various offices and issues. The poll asked about the U.S. Senate race. In November, two Democrats are the only candidates listed, and there is no write-in space. Among likely voters, 20% volunteered that they will leave their ballot blank for U.S. Senate (the pollster did not suggest this idea). Here are the results. Scroll down to page eight for the U.S. Senate race.
In November 2016, when there were also just two Democrats on the ballot for U.S. Senate, 16% of the voters left U.S. Senate blank.