McCain -- the Republican presidential nominee in 2008 and the top Republican on the Senate Armed Services Committee -- said Thursday on NBC's "Today" show the Obama administration has pursued a "feckless foreign policy."
"What this is all about is American weakness and the president's inability to lead," he said.
"There is a belief in the Middle East that the United States is weak and withdrawing, and that's why you're seeing various countries and their leaders reacting," he said. "They have to live in the neighborhood and they believe the United States is leaving and this leadership is in a vacuum."
He cited the situations in Iraq, Iran and Syria as particularly problematic for the United States.
A day earlier, in the wake of Stevens' death, McCain refrained from criticizing the president, saying in a speech on the Senate floor, "There will be plenty of time to talk about who said what and did what, but the fact is, this was a planned attack by radical extremists and it's a great tragedy."
Stevens was killed Wednesday when Islamist protesters overtook a lightly guarded U.S. Consulate in Benghazi, Libya. Stevens had traveled to the region to help organize and legitimize the rebel uprising against former dictator Moammar Gadhafi, which began in Benghazi.
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