Tom Fitton Twat - Obama knew. And, yes, he can still be impeached for his abuse of @RealDonaldTrump #Spygate.
https://twitter.com/TomFitton/status/1220853137768157184
Technically, it is probably the case that Congress could impeach a President who had left office in order to prevent them from holding future office in the Federal government. This would not only prevent a one-term president from returning to seek another term at a later time, but would prevent a former president from running for Congress or serving in the cabinet of a future president or as a federal judge or Supreme Court justice.
https://www.quora.com/USA-Can-a-President-be-impeached-after-leaving-office
William Murphy - College Professor at State University of New York at Oswego