President set free Green swapping sides? (9)

I believe the answer is:

roosevelt

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'president' is the definition.
(Theodore Roosevelt or Franklin Delano Roosevelt)

I cannot understand how the remainder of the clue works.

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(Other definitions for roosevelt that I've seen before include "Surname of 26th and 32nd US presidents" , "Name of two twentieth century US presidents" , "See president" , "Old president" , "Long-term leader" .)

I've seen this clue in The Independent.

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