In Washington, Kerry said Assad had used chemical weapons 11 times, including once last spring. At that time, he said, Obama did not have a "compelling" enough case to push for a U.S. military response.
As for the most recent chemical weapons attack, Kerry declared that "only the most willful desire to avoid reality can assert that this did not occur as described or that the regime did not do it. It did happen - and the Assad regime did do it."
Few if any members of Congress dispute the administration's claim that Assad was responsible for the attack, and lawmakers in both parties appear far more focused on determining how they should respond.
Gaveling the House committee hearing to order, Rep. Ed Royce, R-Calif., said that while it would be important to deter the use of chemical weapons by Assad and others, there remained many unanswered questions, including what the U.S. would do if Assad retaliated.
"The administration's Syria policy doesn't build confidence," he said.
In a letter to her rank and file, Democratic Leader Nancy Pelosi of California said she had received suggestions for legislation in the House "to add language to prevent boots on the ground, to tie the authorization more closely to the use of chemical weapons and to address concerns about an open-ended timetable."
In his comments in Sweden, the president sought to shift the onus for responding to Assad to Congress and the world at large. "I didn't set a red line. The world set a red line" with a treaty banning the use of chemical weapons. He added that "Congress set a red line" when it passed legislation a decade ago demanding Syria stop production of weapons of mass destruction.
His comments drew a disbelieving response from one Republican back home.
"He needs to go back and read his quote," Sen. Saxby Chambliss of Georgia said, referring to a comment the president made slightly more than a year ago. On Aug. 20, 2012, Obama said, "We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. . . . "That would change my calculus" about military action, he added at the time.
In addition to his remarks at a news conference on Wednesday, Obama also likened the challenge confronting the United States and the world with regard to Syria to the actions of Raoul Wallenberg a Swedish diplomat who saved thousands of Jews from death during the Holocaust. Obama went to the Great Synagogue of Stockholm, where he stood with Jewish leaders and said, "Because he refused to stand by, Wallenberg reminds us of our power when we choose not simply to bear witness, but also to act."
An Associated Press survey of lawmakers indicated many were withholding judgment on legislation.
In the Senate, 17 said they support or are leaning in favor of giving Obama the authority he seeks, with 14 opposed or leaning against.
The other 69 were undecided or their views were not known.