In every presidential election, Democrats and Republicans lob charges and claims about the venerable old-age programs Social Security and Medicare. Older Americans are more reliable voters, and these types of attacks — which at The Fact Checker we call “Mediscare” — appear to have resonance. But caveat emptor — the claims are often misleading. In her first campaign rally as the likely Democratic nominee, Vice President Harris falsely said that the GOP blueprint for governing in a new...