The country’s voting machines are susceptible to hacking, which could be done in a way so that it leaves no fingerprints, making it impossible to know whether the outcome was changed, computer experts told President Trump’s voter integrity commission Tuesday. The testimony marked a departure for the commission, which was formed to look into fraud and barriers to voting, but which heard that a potentially greater threat to confidence in American elections is the chance for enemy actors to meddle. “There’s no perfect security; there’s only degrees of insecurity,” said Ronald Rivest, a professor at the Massachusetts Institute of Technology....