President Obama said Tuesday that the United States had both a "moral obligation" and a "national security interest" in ending the civil war in Syria.
"My job is to constantly measure our very real and legitimate humanitarian and national security interests in Syria, but measuring those against my bottom line, which is what is the best interest of America's security," Obama said at the White House.
He added: "I think we have both a moral obligation and a national security interest in both a) ending the slaughter in Syria and b) ensuring a stable Syria."
Obama has faced criticism from lawmakers who have suggested he risks looking weak after pledging that chemical weapons use represented a "red line."
But Obama pointed to past intelligence failures suggesting Iraq had developed weapons of mass destruction.
"It didn't work out that well," Obama said.
"I don't make decisions based on 'perceived' and I can't organize international coalitions around 'perceived.'"
On Monday, Senate Foreign Relations Committee Chairman Robert Menendez (D-N.J.) introduced legislation that would provide American arms to vetted opposition groups.
White House officials have previously said they are weighing such a plan but remain concerned about the potential risks — including the possibility that American weapons could find their way into the hands of terror groups.
But pressure is intensifying on the White House to respond, with critics of the president saying that inaction undermines American credibility and allows the situation on the ground to worsen.
Sen. John McCain (R-Ariz.) on Sunday called for “game-changing action” in Syria, saying Obama’s “red line” had been definitively crossed.
“The whole thing is escalating,” McCain said on “Fox News Sunday.”
“The whole situation is becoming more and more expansive, and unfortunately the red line that the president of the United States had written was apparently written in disappearing ink.”
Obama said Tuesday the White House was "not doing nothing," noting that the U.S. was working aggressively to provide non-lethal aid and organizational assistance to the rebels in Syria.
"There would be severe costs in doing nothing. That's why we're not doing nothing," Obama said.
Moreover, Obama said, any nation or individual who doubted the resolve of his administration should ask terrorist leader Osama bin Laden and Libyan dictator Moammar Gadhafi about his administration's commitment.
"The international community has a pretty good sense that we typically follow through on our commitments," Obama said.