09/10/2013 04:11 pm ET

'The Presidents' Gatekeepers' On Discovery: Behind Ronald Reagan's 'Tear Down This Wall' Speech (VIDEO)

Discovery Channel's new two-part, four-hour special "The Presidents’ Gatekeepers" (premieres Wed., Sept. 11 and Thurs., Sept. 12 at 9 p.m. ET) takes a look at the power behind the presidency: The White House Chiefs of Staff.

Featuring commentary and never-before-heard stories from all 20 living White House Chiefs of Staff -- spanning nine administrations and more than 50 years -- it's a fascinating look at moments in history from a completely new, insider perspective.

We've got an exclusive sneak peek, above, at an historic moment in recent history: President Ronald Reagan's speech challenging then-Soviet statesman Mikhail Gorbachev to tear down the Berlin Wall to show support for the increased freedoms in the Communist Eastern Bloc.

Reagan's most quoted line from the speech is a powerful one -- "Mr. Gorbachev, tear down this wall" -- but can you believe it almost didn't make it into the final speech? Watch our sneak peek of "The Presidents' Gatekeepers," above, to hear the whole story.

Tell us: Are you surprised to hear this new side of the story? What other epic presidential moments almost didn't happen?

"The Presidents' Gatekeepers" two-night, four-hour event premieres Wed., Sept. 11 and Thurs., Sept. 12 at 9 p.m. ET on Discovery Channel.



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