WASHINGTON — Michael Sussmann, a prominent cybersecurity lawyer with ties to Democrats, was acquitted on Tuesday of a felony charge that he lied to the F.B.I. about having no client in 2016 when he shared a tip about possible connections between Donald J. Trump and Russia.
The verdict was a blow to the special counsel, John H. Durham, who was appointed by the Trump administration three years ago to scour the Trump-Russia investigation for…