Election officials preparing for this year’s midterms have yet another security concern to add to an already long list that includes death threats, disinformation, ransomware and cyberattacks — threats from within. In a handful of states, authorities are investigating whether local officials directed or aided in suspected security breaches at their own election offices. At least some have expressed doubt about the 2020 presidential election, and information gleaned from the breaches has surfaced in conspiracy theories pushed by allies of former President Donald Trump.