(ABC News) -- Stymied by lagging public opinion and an 11th-hour diplomatic curveball, President Obama tonight argued that he still needs congressional authorization for military strikes against Syria even though its possible he may not have to use it.
"America is not the world's policeman. Terrible things happen across the globe, and it is beyond our means to right every wrong. But when, with modest effort and risk, we can stop children from being gassed to death and thereby make our own children safer over the long run, I believe we should act," Obama said during a rare prime-time televised address to the nation.
At the same time, the president said he is willing to explore a new Russian diplomatic proposal to neutralize Bashar al-Assad's chemical weapons, effectively hitting the pause button on an aggressive push for a vote this month that would allow him to launch a military strike on Syria.
"I'm sending Secretary of State John Kerry to met his Russian counterpart on Thursday, and I will continue my own discussions with President Putin," Obama said. He said the administration was drafting a U.N. Security Council resolution that would require Assad to unilaterally disarm and destroy his chemical weapons.
In the meantime, Obama said, the U.S. military would stay at its current posture to keep up pressure on Assad and prepare to strike if this last-ditch diplomatic overture fails.
"Our ideals and principles, as well as our national security, are at stake in Syria," he said, "along with our leadership of a world where we seek to ensure that the worst weapons will never be used."
Obama has been trying to thread the diplomatic needle, seeking to preserve American and international credibility on chemical weapons with a tough line against Assad while simultaneously convincing the American public that he doesn't want a wider war and would actually prefer a diplomatic solution.
Tonight, he sought to directly address popular concerns about military action, giving answers to questions he received in letters from average Americans.
He denied that U.S. intervention would be anything like Iraq or Afghanistan, calling it a "limited" strike to send a message, not take out a dictator. He dismissed concerns about possible retaliation from Assad, saying the Syrian military could not "seriously threaten our military" or allies.
Obama said he ultimately concluded that the use of chemical weapons in Syria represents a unique case that requires American leadership on a global level.
"The world saw in gruesome detail the terrible nature of chemical weapons and why the overwhelming majority of humanity has declared them off limits, a crime against humanity and a violation of the laws of war," he said.
"As the ban against these weapons erodes, other tyrants will have no reason to think twice about acquiring poison gas and using them," he said. "Over time our troops would again face the prospect of chemical warfare on the battlefield, and it could be easier for terrorist organizations to obtain these weapons and to use them to attack civilians."
But so far the president isn't winning over many people with his argument -- in fact, he's losing it. In both the House and Senate, more members are now opposing Obama on Syria than supporting him.
Earlier in the day, Obama personally made his case to all senators on Capitol Hill, lunching first with the Democrats, then Republicans. Since Friday, the president and his team have directly lobbied nearly 450 members of the House and Senate, including private briefings for key members in the White House situation room, calls from Air Force One and nearly a dozen classified briefings.
In recent days, Obama has conceded that he may ultimately fail to turn public opinion, which is still strongly against military intervention in Syria despite more than a week of lobbying on Capitol Hill and speaking directly to the American people.
The effort, the most intense of Obama's presidency, may be the biggest test yet of his leadership: Asking for support on a national security issue and failing to get it, would make him look weak around the world and like a lame duck at home.
Above all, what the president does not want is for Congress to undercut his efforts internationally by voting to reject his Syria resolution. So the president today asked Senators to wait a bit before voting -- to give him more time -- to work on diplomacy, but more importantly, to work on lining up votes.