Federal prosecutors filed three briefs late on Friday portending grave danger for three men: the former Trump campaign chair Paul Manafort, the former Trump fixer Michael Cohen, and President Donald Trump. In an age when Americans usually get mere squibs of breaking news from Twitter, Facebook, and red-faced cable shouters, many started their weekend poring over complex legal filings and peering suspiciously at blacked-out paragraphs. The documents were stunning, even for 2018.