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After a big political handshake yesterday between U.S. President Barack Obama and Russian President Dmitry Medvedev on cooling nuclear bravado, an insistent Iran plays show-and-tell with a new advanced centrifuge system.

In their interview, part of which we ran in last night's Block 4 and part of which is embedded below, George Stephanopoulos asks the president about whether sanctioning Iran would work and the unpredictable leader like Iranian President Mahmoud Ahmadinejad, who recently called Obama an "inexperienced amateur."

"The guy's known for saying some pretty, pretty unconstructive stuff, how's that? And offensive stuff," Obama said. "So I don't take that seriously."