The question of how Donald Trump won the 2016 election looms over his presidency. In particular, were the 78,000 voters who gave him an Electoral College victory affected by the Russian trolls and hackers? Trump has denied it. So has Vladimir Putin. Others cast the answer as unknowable. In Cyberwar, Kathleen Hall Jamieson marshals the troll posts, unique polling data, analyses of how the press used hacked content, and a synthesis of half a century...