Even if he were willing to consider such a scenario, Obama said, the Syrian people would never accept it.
"It is unimaginable that you can stop the civil war here when the overwhelming majority of people in Syria consider him to be a brutal, murderous dictator," Obama said. "He cannot regain legitimacy."
Bloomberg reported Thursday that Russian officials were increasingly confident the U.S. and France were ready to agree on coordinating efforts to fight Islamic State, perhaps including Assad's forces.
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Obama has said that Assad's status remained a sticking point to such coordination with Russia, and that the U.S. would continue to evaluate whether Russia was serious about focusing its military strikes against Islamic State instead of those forces battling Assad.
As talks continue in Vienna aimed at defining the political solution, Obama said Assad's backers in Russia and Iran need to make a final choice, whether to continue to "prop up Assad," or to "save the Syrian state and work with the international community … to find a government that can be truly legitimate." He said it could take months for Russia, Iran and the Syrian regime to recognize that a political solution including Iran was untenable.
The president's comments came as he sat down for the first time with Canada's new prime minister, Justin Trudeau, on the sidelines of the APEC Summit in Manila.
The young Canadian premier reiterated that he would fulfill his campaign pledge to end his country's limited air campaign against Islamic State, but that they would do "more than its part to defend against" the militant group, including an increased deployment of forces to train local fighters.
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