President Obama sees executive action as the primary way to build his legacy, but years from now, he could regret his penchant for going it alone. By so frequently testing the limits of his executive authority, Obama has set a precedent for future White House occupants to bypass Congress with even more regularity, say legal scholars and political insiders. A President Hillary Clinton or Jeb Bush, for example, could point to Obama as the model for interpreting “prosecutorial discretion,” taking a similar position on whether their administration would enforce laws conflicting with their political aspirations. Obama used executive action to...