In a high-stakes address to the nation Tuesday night, President Barack Obama cautiously embraced a diplomatic effort to rid the Syrian regime of its chemical weapons, but urged the nation to stand with him in his resolve to launch a military strike if that effort fails.

The president said he asked Congress to hold off on voting to authorize strikes to give the diplomatic effort a chance to work, but indicated he was willing to act if it does not. Though it’s an open question whether he was able to sway public sentiment on the issue of a strike, many members of Congress did not appear to be moved by his pitch that the Syrian chemical attacks were not just an affront to humanity but could also lead to future security risks to the United States.

“Our ideals and principles as well as our national security are at stake in Syria, along with our leadership of a world where we seek to ensure that the world’s worst weapons will never be used,” he said.

“America is not the world’s policeman,” he said, noting concerns from Americans to that effect. “But when, with modest effort and risk, we can stop children from being gassed to death, and thereby make our own children safer in the long run, I believe we should act. That’s what makes America different. That’s what makes America exceptional.”

Obama told the nation that there was no doubt the Syrian regime gruesomely massacred its own citizens, and asked the country to view the hundreds of videos and pictures of the dead and dying.

“When dictators commit atrocities, they depend upon the world to look the other way,” Obama said. “The question now is what is the United States of America and the international community are going to do about it.”

Failure to act would embolden countries like Iran to develop other weapons of mass destruction, Obama said, and eventually make it easier for terrorists to acquire chemical weapons as well.

“This is not a world we should accept,” he said.

The president also sought repeatedly to appeal to a nation where public opinion is overwhelmingly against a new war — saying that he would insist that the strikes be targeted but effective.

“I will not put boots on the ground in Syria,” he said. “I will not pursue a prolonged air campaign like Libya or Kosovo.” And he said that Syria was no match for the United States military if it tried to retaliate, and Bashar al-Assad knows that.

“Neither Assad nor his allies have any interest in escalation that would lead to his demise,” Obama said.

Obama also addressed concerns about some of the rebels fighting Assad linked to al-Qaida.

“Al-Qaida will only draw strength in a more chaotic Syria if people there see the world doing nothing to prevent innocent civilians from being gassed to death,” Obama said. “The majority of the Syrian people, and the Syrian opposition we work with, just want to live in peace, with dignity and freedom. And the day after any military action, we would redouble our efforts to achieve a political solution that strengthens those who reject the forces of tyranny and extremism.”

The president’s speech may effect public opinion, but votes in Congress are another matter. Numerous Republican lawmakers in particular have put out statements in the past few days either opposed to a strike or highly critical of the president’s approach. Immediately after the speech, few lawmakers appeared to be swayed, judging by the flurry of statements being sent out.

On MSNBC, Sen. Joe Manchin III, D-W.Va., made another pitch for the alternative resolution he drafted with Sen. Heidi Heitkamp, D-N.D., that would give Syria time to give up its chemical weapons before facing a possible strike.

The president would have lost a vote on the strike authorization he has sought, Manchin suggested.

“The support is just not there,” he said.

Sen. Rand Paul, R-Ky., responded with his own video ripping the president’s proposal.

“Twelve years after we were attacked by al-Qaida, 12 years after 3,000 Americans were killed by al-Qaida, President Obama now asks us to be allies with al-Qaida,” he charged. “Americans, by a large majority, want nothing to do with the Syrian civil war. We fail to see a national security interest in a war between a leader who gasses his own citizens and Islamic rebels who are killing Christians.”

Sen. Charles E. Grassley, R-Iowa, said he continues to lean against an authorization to use force.

“I don’t think the case for military action has been made,” he said, despite briefings at the White House, a visit from the president to the Capitol earlier Tuesday or his speech. Grassley said his concerns and those of Iowans haven’t yet been answered. “If the goal is to deter and degrade Assad’s ability to use chemical weapons, how would a limited strike achieve this goal? What are the risks of military action? What is the U.S. national interest in striking Syria?”

Of course, it remains an open question whether Congress will ever vote on a Syrian authorization given the new diplomatic effort — and what appears to be a lack of votes.

“After this impassioned plea I cannot imagine Pres Obama not launching military strike if diplomacy fails, regardless of what Congress does,” tweeted Sen. Lindsey Graham, R-S.C. Graham, along with Sen. John McCain, R-Ariz., has led the effort to back the Syrian rebels.

In a joint statement, Graham and McCain said they regret that Obama “did not speak more forcefully about the need to increase our military assistance to moderate opposition forces in Syria, such as the Free Syrian Army.”

They also said Obama should have laid out a clear plan to test the seriousness of the Russian diplomatic proposal, preferably by bringing a resolution to a vote in the United Nations Security Council.