Former Vice President Mike Pence, a longtime leader of the anti-abortion movement, has taken up a lonely crusade to defeat the nomination of Robert F. Kennedy Jr. for health secretary. His organization, Advancing American Freedom, is running ads against Mr. Kennedy. Mr. Pence has accused Mr. Kennedy of promoting “abortion on demand.” His fellow abortion opponents are not listening. Thousands of anti-abortion activists descended on Washington on Friday to mark the 52nd anniversary of Roe v. Wade, the Supreme Court case that established a constitutional right to abortion. President Trump addressed the crowd at the March for Life by video....