The former Florida congressman was found guilty of cocaine possession.
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Former Florida Gov. Jeb Bush and Sen. Rand Paul (Ky.) run a close second.
Obama said he was hopeful a deal could be negotiated after Republican primaries.
Fifty-one percent of district voters said his scandal would prevent them from voting for him.
The former CIA director praised Hillary Clinton for supporting controversial CIA activities.
Obama declined to say who he would prefer in 2016.
"It's all nonsense," Putin said.
Sen. Warren's memoir A Fighting Chance is due to be released next week.
"It would give every excuse for the president to move," said Rep. Mario Diaz-Balart.
Obama acknowledged they "sometimes sound like a broken record" on the economy.