Alexander Vindman on Saturday tweeted that he's certain he "did (his) duty" as a key witness in President Donald Trump's impeachment inquiry. "One year since The Call. Much has changed for me and so much more has changed for our country. I rest well knowing I did my duty," Vindman, former top Ukraine expert at the National Security Council, wrote. Groundwork for the impeachment began when Democrats announced an impeachment inquiry following an anonymous whistleblower complaint alleging Trump sought election help from Ukrainian President Zelensky in a phone call. The Senate ultimately voted to acquit Trump on two articles of...