On Wednesday, President Biden lunched with Senate Democrats, hosted governors and mayors for a roundtable on infrastructure and also — hung out with Olivia Rodrigo, an 18-year-old pop star beloved by Generation Z. Rodrigo, who currently has the No. 1 album in the country and whose song "Drivers License" has been a radio staple for months, recorded public service announcement videos with Biden and Dr. Anthony Fauci and made an appearance in the White House briefing room to promote coronavirus vaccines. Her visit underscores one of the roadblocks to vaccinating more Americans right now. Only about 42 percent of people...