"They also have work to do with respect to shoring up the facts of what happened," Thompson said.
The Senate Foreign Relations Committee plans a meeting Tuesday, according to its chairman, Sen. Bob Menendez, D-N.J. The Senate Armed Service Committee will gather a day later, said Oklahoma Sen. Jim Inhofe, the top Republican on the panel.
Kerry confidently predicted that lawmakers would back limited military strikes.
"The stakes are just really too high here," he said.
Kerry was asked repeatedly in the broadcast interviews what Obama would do if Congress didn't give its consent. He said he believed lawmakers would recognize the grave implications for letting a chemical weapons attack go unchecked and what that might mean for U.S. efforts to force North Korea to get rid of its nuclear weapons and prevent Iran from acquiring such capability.
"We are not going to lose this vote," Kerry said. "The credibility of the United States is on the line."
Obama is likely to find stronger support in the Democrat-controlled Senate than the GOP-dominated House, yet faces complicated battles in each. Some anti-war Democrats and many tea party-backed Republicans are opposed to any intervention at all, while hawks in both parties, such as McCain, feel the president must do far more to help Syria's rebels oust Assad from power.
"It can't just be, in my view, pinprick cruise missiles," McCain told CBS' "Face the Nation."
In an interview with an Israeli television network, McCain said Obama has "encouraged our enemies" by effectively punting his decision to Congress. He and fellow Republican Sen. Lindsey Graham of South Carolina have threatened to vote against Obama's authorization if it is too limited.
On the other end of the spectrum, an unusual coalition of foreign policy isolationists, fiscal conservatives and anti-interventionists in both parties opposes even limited action for fear that might draw the United States into another costly and even bloody confrontation.
The White House request to Congress late Saturday speaks only of force to "deter, disrupt, prevent and degrade" the Assad regime's ability to use chemical weapons.
"I think it's a mistake to get involved in the Syrian civil war," said Sen. Rand Paul, R-Ky.
Echoing that sentiment, Sen. Chris Murphy, D-Conn., questioned, "Does a U.S. attack make the situation better for the Syrian people or worse?"
Paul expected the Senate to "rubber-stamp" Obama's plan, while he said it was "at least 50/50 whether the House will vote down involvement in the Syrian war." Inhofe predicted defeat for the president.
Despite the intense gridlock in Congress over debt reduction, health care, immigration and other issues, some lawmakers were more optimistic about the chances of consensus when it came to a question of national security.
Rep. Peter King, R-N.Y., who criticized Obama for not proceeding immediately against Assad, said he'd vote "yes" and believed the president should be able to build a House majority over the next several days.
"At the end of the day, Congress will rise to the occasion," added Rep. Mike Rogers, R-Mich. "This isn't about Barack Obama versus the Congress. This isn't about Republicans versus Democrats. This has a very important worldwide reach."
Sen. Tim Kaine, D-Va., said Congress and the American people would support action once Obama finishes making his case. Sen. Saxby Chambliss, R-Ga., said if Obama doesn't do that, he won't get his authorization.
"He's got to come out and really be in-depth with respect to the intelligence that we know is out there," said Chambliss, the top Republican on the Senate Intelligence Committee. "He's got to be in-depth with respect to what type of military action is going to be taken and what is our current strategy."
At the Capitol, Sen. Jeff Sessions, R-Ala., said Obama's proposed resolution needed tightening. "I don't think Congress is going to accept it as it is," he said.