Former President Barack Obama invoked Nazi Germany to urge attendees of a Q&A session to remain vigilant in today's political age, according to a journalist who attended the event.

Crain's Chicago Business reporter Greg Hinz attended the event at the Economic Club of Chicago where Obama was quizzed by Ariel Investments President Mellody Hobson about his beliefs on a variety of subjects.

Obama said the United States had survived tough times before and could do so again, mentioning the age of McCarthyism and the attempted impeachment of former President Richard Nixon as examples.

The two-term Democrat expressed the importance of a free press and urged the country not to "grow complacent," saying "we have to tend to this garden of democracy or else things could fall apart quickly."

Hinz writes Obama then brought up the specter of Adolf Hitler, who came to power in Democratic Germany amid the financial crisis of the 1930's.

"Sixty million people died…" he reports Obama said. "So, you've got to pay attention. And vote."

On Twitter, Hinz called the comments "remarkable" and framed them as a rebuke of current president Donald Trump.