A man acting erratically on a train headed for Chicago was spotted by a rail worker who called police. Officers found guns and a pamphlet about crowd control in his carry-on bag — and a plan for a mass casualty event. Almost two years later, federal authorities say the man charged with attempting to assassinate President Donald Trump at the White House Correspondents Association dinner on Saturday was arrested with a shotgun and a semiautomatic pistol he brought with him to Washington, D.C., on an Amtrak train from California. It's just the latest security incident involving long-distance public ground transportation — and it won't be the last unless Amtrak and other companies find a way to address passenger screening and security at their stations, union officials who represent on-train employees say. An Amtrak spokesperson declined to discuss security or to say whether Cole Tomas Allen followed the company's protocol for transporting firearms.…