WASHINGTON — The assassination attempt against former President Donald Trump at a Pennsylvania rally in July was “preventable and should not have happened,” according to a bipartisan House panel that is investigating the shooting and what it calls the “stunning security failures” at the event. The report from a House task force, released Monday, is just the latest look at the cascading and wide-ranging law enforcement failings that preceded the July 13 shooting at the Butler, Pennsylvania, rally where Trump was struck in the ear by gunfire.