9:19 p.m. ET - CNN's Jessica Yellin tweets: "American exceptionalism: @BarackObama often accused of apologizing for America, makes case for using America's mil might to defend values."
9:17 p.m. ET - White House Deputy Press Secretary Eric Schultz tweets: "President Obama: "The burdens of leadership are often heavy, but the world is a better place because we have borne them."
9:15 p.m. ET - Obama asks what kind of world we would live in if we watch a leader violate international law with poison gas and "look the other way."
9:14 p.m. ET - CNN's Jim Acosta tweets: "Obama confirms he's asked Congress to "postpone" a vote while Russia proposal takes its course."
9:13 p.m. ET - Obama said it's too early to tell if the latest diplomatic efforts will succeed, but there is now the possibility that Syria will be rid of chemical weapons "without force." As part of those efforts, he said he asked Congress to put off any votes on action and will send Kerry to meet with Lavrov this week.
9:12 p.m. ET - Obama said he agrees the US should not be the world's policeman and said he has a "deeply held preference for peaceful solutions." But the United States "does not do pinpriks."
9:08 p.m. ET - The White House tweets: "Obama: "I have spent 4.5 years trying to end wars---not start them. Our troops are out of Iraq. Our troops are coming home from Afghanistan."
9:09 p.m. ET - Addressing criticism of a potential strike, including one veteran that wrote to the president saying "this nation is sick and tired of war," Obama said he will "not put American boots on the ground," "not pursue an open ended action" and "not pursue a prolonged air campaign." Instead, it would be a "targeted strike."
9:07 p.m. ET - Obama said he determined the US should respond militarily to Assad to deter future action, degrade his ability and make clear the US will not tolerate their use. "That's my judgment as commander of chief," he said. But as president of the world's oldest constitutional democracy, he also felt it was right to bring the decision to Congress.
9:05 p.m. ET - Obama outlined the evidence that led to the conclusion that Assad used chemical. "These things happened. The facts cannot be denied." Now he said, the question is what the US and the international community is "prepared to do about it."
9:02 p.m. ET - Obama said he resisted calls for military action in Syria "because we cannot solve someone else's civil war through force." But the situation "profoundly changed on August 21st." He said the images were "sickening."
9:01 p.m. ET - Obama, standing in the East Room, says he will talk about Syria tonight "why it matters and where we go from here." over the past 2 years.
8:05 p.m. ET - @JohnKingCNN reports the president will not lay out a timetable for diplomacy or potential military action in his address tonight, according to a senior administration official involved in the speech process. The administration believes it can't make those calculations until the Kerry-Lavrov meeting Thursday, the initial eye-to-eye test of whether Russia and the Syrians are serious. Any discussion of when to schedule votes, this official said, should wait until the Kerry-Lavrov meeting, "which will give us a sense of what those alternative resolutions should look like."
The president, in his meeting with lawmakers today, said they should not do anything to take the credible military threat off the table.
7:45 p.m. ET - Former Secretary of State Hillary Clinton, speaking at the National Constitution Center Tuesday night, said Assad's use of chemical weapons violates a universal norm at the heart of our global order that requires a "response from the international community led by the U.S."
"This debate is good for our Democracy," Clinton said in Philadelphia. "Fervent arguments are the lifeblood of self government."
7:38 p.m. ET - Sen. Manchin on @OutFrontCNN said there is less of a risk now from inaction than there would have been from a U.S. military strike on Syria. The moderate Democratic senator said he has always believed the U.S. should go down a "diplomatic course."
7:30 p.m. ET - @eliselabottcnn reports that when Secretary Kerry meets with Russian Foreign Minister Sergey Lavrov, he will begin to discuss a possible deal on Syria's chemical weapons, according to senior state department officials. Kerry will bring a team of experts with him for the talks, which begin Thursday and are expected to take place in several sessions over two days, the officials said. The officials cautioned the negotiations may not be concluded in Geneva during the first set of talks. The officials said a final deal, whenever it is reached, would then be taken to the United Nations to be enshrined in a Security Council resolution.
7:13 p.m ET - @barbarastarrcnn reports the Defense Department has not yet been involved in the turnover of chemical weapons by Syria, according to a senior US military official. However, military and civilian experts are informally looking at what they might do.
7:01 p.m. ET - Reports @JimAcostaCNN: In his speech tonight the president will address why the situation in Syria is in the US' national interests, why it is in the US' interests that Syrian President Assad be be held accountable for the use of chemical weapons, that the military response would be limited in duration and scope and that the White House sees a "diplomatic opportunity" in the recent Russian proposal for Syria to rid itself of its chemical weapons.
6:49 p.m. ET - @RickSantorum on @CrossfireCNN said the US has no national security interests in Syria. "There's a big difference between action and military action," Santorum said. "I'm for action, I'm just not for a military strike."
6:32 p.m. ET - Former Sen. Joe Lieberman on @CrossfireCNN said he wished the US "were not pausing" in Syria. He said the president made the right decision to draw the red line and was "disappointed when he decided to toss it to Congress."
6:28 p.m. ET - CNN's Adam Aigner-Treworgy tweets: "On @CNNSitRoom @jonfavs says to expect POTUS to speak for about 15 minutes."
6:28 p.m. ET - On @CNNSitRoom @jonfavs said Obama will be "firm" tonight in his remarks. "He'll make the case ... be passionate about what's at stake here."
6:25 p.m. ET -- @jonfavs, Obama's former speechwriter, told @wolfblitzercnn tonight's speech is "just about ready" and that the president often stays up "very late at night" making corrections himself.