Michael D'Antonio is the author of the book Never Enough: Donald Trump and the Pursuit of Success and co-author, with Peter Eisner, of the book High Crimes: The Corruption, Impunity, and Impeachment of Donald Trump. The opinions expressed in this commentary are his own. View more opinion on CNN.
(CNN)The question arose the minute federal agents began their search of Rudy Giuliani's home and office. Once again someone close to former President Donald Trump -- someone who could testify against the former president -- was in prosecutors' crosshairs. Once again it seems possible that a Trump friend could flip into an enemy.