Challenger Marina Silva (left) and incumbent Dilma Rousseff face off during a presidential debate in Aparecida, Brazil, in September. Sebastiao Moreira/EPA/Landov hide caption

itoggle caption Sebastiao Moreira/EPA/Landov

New Jersey Gov. Chris Christie turns to leave a news conference at the Statehouse in Trenton on Tuesday after he announced that he will not run for president in 2012.

Mel Evans/AP hide caption

itoggle caption Mel Evans/AP