"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.
6:23 p.m. ET - @LisaDCNN reports Senate Majority Leader Harry Reid, on the Senate floor, said he's canceling the planned the planned briefings for senators Wednesday because there are too many moving targets.
6:07 p.m. ET - @deirdrewalshcnn asked Democratic Sen. Carl Levin, chairman of the Senate Armed Services Committee, if the president gave a timeline for the diplomatic efforts under consideration.
"I don't know he put a specified period on it. He thought it could be fairly short, that it would be obvious. Fairly short period of time where it would be clear whether Russia is going to come through as they said they would, and whether Syria was going to get rid of their chemical weapons."
5:43 p.m. ET - @JimAcostaCNN reports on the president's meetings with Republican and Democratic senators today: "The President said his administration would spend the days ahead pursuing this diplomatic option with the Russians and our allies at the United Nations. In the meantime, the President said his administration would work with members of Congress on authorizing language," according to a White House official.
5:33 p.m. ET - Sen. Paul told @wolfblitzer "there's a potential" for these negotiations to have an impact on the chemical weapons in Syria, whereas military action would not.
5:29 p.m. ET - On @CNNSitRoom: Kentucky Republican Sen. Rand Paul said one of the reasons diplomatic avenues are now being pursued is because "people like me prevented the use of force."
5:08 p.m. ET - CNN's Lisa Desjardins tweets: "FROM MOSCOW: Russian TV says that Syria is now ready to disclose all locations of chemical weapons stores, according to our Nick Paton Walsh."
4:56 p.m. ET - Sen. Joe Manchin, a Democrat from West Virginia, was one of the senators who met with the president today. Responding to reporters on Capitol Hill, Manchin, who opposes the president's plan, said Obama wants to "keep his finger on the pulse if you will and on the trigger if needed."
4:40 p.m. ET - On @TheLeadCNN: Obama's task tonight, according to @David_Gergen: "easy speech to write" and a "hard speech to sell."
4:39 p.m. ET - On @TheLeadCNN: Michael Gerson, a former speechwriter for President George W. Bush, said President Obama needs to "establish his resolve" with tonight's speech and "hold out the possibility that things can get better through negotiation."
4:38 p.m. ET - CNN's Dana Bash tweets: "big pic takeaway from potus to senators in private lunches today: dont vote now b/c we need the threat of force & a failed vote would hurt."
Bash adds: "also told POTUS meeting w/ Senate Repubs wasnt political. V sober and respectful on both sides."
4:31 p.m. ET - On @TheLeadCNN: Rep. Tulsi Gabbard, a Democrat from Hawaii, who does not support the president's plan, said she supports the delay in the Senate vote and called today's diplomatic developments a "positive development."
4:29 p.m. ET - On @TheLeadCNN: Rep. Adam Kinzinger, a Republican from Illinois, who supports the president's plan for intervention in Syria, said there should be a timetable associated with diplomatic steps to ensure stall tactics are not being used.
4:24 p.m. ET - CNN's Lisa Desjardins tweets: "Russian withdrawal: Russia dropped its request for an emergency UN Security Council meeting due to 'changing circumstances' a UN source says."
4:18 p.m. ET - Eight additional countries signed on to the joint statement condemning the use of chemical weapons released during last week's G20 conference in Russia, according to the White House. The addition of Georgia, Guatemala, Kuwait, Malta, Montenegro, Panama, Poland and Portugal brings the total to 33 countries.
4:10 p.m. ET -- Tonight will be President Obama's 9th address to the nation and the 4th delivered from the East Room. Previous East Room addresses: after the raid that killed Osama bin Laden (5/1/11), to address the draw down of forces in Afghanistan (6/22/11) and to speak about the national deficit and the debt limit (7/25/11).
3:58 p.m. ET - @eliselabottcnn: Secretary of State Kerry will travel to Geneva on Thursday to meet with Russian Foreign Minister Lavrov to discuss Syria, according to a senior State Department official.