In a rare prime-time address to the nation Tuesday, President Obama forcefully argued that preventing Syria’s regime from using chemical weapons is critical to U.S. interests and urged lawmakers to back military force against Damascus even as he pursued a last-ditch diplomatic solution.

"When dictators commit atrocities, they depend on the world to look the other way, but these things happened. The facts cannot be denied," Obama told the nation, charging Syrian President Bashar Assad with using chemical weapons against civilians. "The question now is what the United States and the international community is prepared to do about it."

"What kind of world will we live in," Obama asked, if the United States allows a dictator to go unpunished after "brazenly" using chemical weapons on his own people.

The president also said that he had a “preference for peaceful solutions,” and would pursue a diplomatic resolution offered by Russia. But he warned that his patience was limited and that that he would press military action against the Syrian regime if a deal did not materialize soon.

“It's too early to tell whether this offer will succeed,” Obama cautioned. “Any agreement must verify that the Assad regime keep its commitment.”

But the president said the Russian proposal was worth pursuing if Syria would give up its chemical weapons without the use of force. Obama said he had asked lawmakers to delay votes on measures authorizing military action to allow diplomacy to proceed.

Obama's Tuesday evening address was originally scheduled as part of a White House full-court press for Congress to grant their approval for military strikes to punish Assad for using chemical weapons in that country's civil war.

A Senate vote was initially expected to take place Wednesday, but the last 48 hours opened the door to a possible peaceful resolution after Russia offered to help Syria hand over its chemical arsenal to international inspectors.

In his address from the East Room, Obama faced a challenging task: urging a skeptical public and hesitant lawmakers to back military action against Syria, while also pursuing a possible negotiated settlement.

Obama argued that leaving Assad unchecked would encourage others to use chemical weapons, potentially even against U.S. troops or on American soil.

Obama said the use of these banned weapons would erode prohibitions on other weapons of mass destruction, including nuclear weapons.

Acknowledging that Americans are tired of wars In Iraq and Afghanistan, Obama said he had spent “four and a half years working to end wars, not to start them.”

He promised that any military action in Syria would be limited but strong enough to deter Assad from using such weapons again, noting that the U.S. military “doesn’t do pinpricks.”

“Even a limited strike will send a message to Assad that no other nation can deliver,” he said. “I don't think we should remove another dictator with force – we learned from Iraq that doing so makes us responsible for all that comes next. But a targeted strike can make Assad, or any other dictator, think twice before using chemical weapons.”

"I've ordered the military to maintain their current posture to keep the pressure on Assad," Obama said, arguing that the threat of military force led to the Russian offer.

Secretary of State John Kerry will sit down with Russian Foreign Minister Sergei Lavrov in Switzerland Wednesday to discuss a possible deal, including timelines and conditions for inspections of Syria’s weapons to take place.

Kerry first floated the idea of giving Assad a last chance to avert a strike by handing over chemical weapons to international control on Monday. The Russian foreign minister quickly seized on the idea and pulled Syria on board.

With polls showing a majority of the public deeply opposed to a Syria strike and Congressional votes in favor of granting Obama military action diminishing by the day, Obama cautiously welcomed the Russian offer.

The Republican National Committee wasted little time in criticizing Obama's speech.

“The administration's handling of the U.S. response to Syria has been so haphazard it's disappointed even the president's most ardent supporters,” RNC Chairman Reince Priebus said in a statement.

“This rudderless diplomacy has embarrassed America on the world stage. For a president who campaigned on building American credibility abroad, the lack of leadership coming from the Oval Office is astounding,” he added.

Sen. Rand Paul, R-Ky., a strong critic of Obama’s foreign policy and an opponent of military action against Syria delivered a personal response to the president’s speech.

Paul said Obama had presented no clear objective in Syria.

“I see no clear ally for America on either side of this civil war,” he said.

Obama's willingness to let Russia's offer of a diplomatic solution play out, however, won him praise from some on the left.

“Public pressure worked. The American people knew that diplomacy was a credible and strategic option, and this great news from the President Obama will be better for America and his presidency than dropping bombs on Syria,” the Progressive Change Campaign Committee said in a statement after the speech.

Obama’s speech Tuesday followed a rare visit to Capitol Hill in the afternoon, where he huddled behind closed doors first with Senate Democrats and then Senate Republicans, explaining his stance on Syria.

Senate Majority Leader Harry Reid, D-Nev., had already postponed the planned Wednesday vote in the upper chamber, but Obama also asked his former colleagues to delay it indefinitely to allow the administration time to pursue a diplomatic solution.

After the meeting, Reid said he wouldn't be held to any “artificial deadline,” and called for negotiations to take precedence.

“It's important we do this well, not quickly,” he told reporters. “In the last 24 hours there's been remarkable changes. Let's see what else happens.”

Barbara Boxer, a California Democrat who sits on the Senate Foreign Relations Committee, heaped praise on Obama after the lunch meeting for keeping the pressure on Syria and gave him credit for bringing Russia and Syria to the point where she said they are ready to negotiate a diplomatic solution.

“We will give diplomacy a chance to work,” she said. “And I hope that the Russians meant it when they said let's try to resolve that in a way that would result in the absolute destruction of Syria's chemical weapons.”

A diplomatic outcome though faces many challenges. As Obama was meeting with Democrats earlier Tuesday, Russian President Vladimir Putin said the offer would only work if the U.S. agrees to take the use of force off the table – a call likely to undercut the administration’s support for the plan.

Russia’s foreign ministry also expressed concern about implementing the Syria deal through a binding UN resolution, which Kerry said would be necessary.

As the Obama administration began to engage Russia and Syria on the offer, lawmakers appeared split about the prospects for success.

“The Russia development — we're waiting to see if it plays out,” Sen. Max Baucus, D-Mont., told the Washington Examiner. “We're waiting to see where the beef is — if they're serious or they're not serious. It's deeds not words that count here.”

Sen. James Risch, R-Idaho, said Obama should engage with the Russians despite reservations about Moscow’s credibility.

“Anything is better than pulling the trigger at this point,” he said. “I think this is something that needs to be seriously considered and not dismissed out of hand even though it is the Russians you're dealing with."

But Sen. Joe Manchin, D-W. Va., was more reluctant to work with Russia.

“Obama said he wants to make sure that they are serious brokers and serious players and it's not just rhetoric,” he said. “I oppose allowing Russia to take the diplomatic lead on this.”