Obama, who arrived in Stockholm early Wednesday, was hoping to maintain the momentum toward congressional approval that he has generated since Saturday, when he announced he would ask lawmakers to authorize what until then had appeared to be imminent military action against Syria.
On Monday, the president met privately at the White House with the Senate's two leading Republican hawks, McCain and Lindsey Graham of South Carolina, and persuaded them to support his plans for an intervention on condition that he also seek to aid the Syrian rebels seeking to oust Assad.
A day later, he sat down with Boehner, Cantor and several other senior lawmakers to make a similar case that Assad must be punished for breaching the nearly century-old international taboo of using chemical weapons. After gaining significant support, Kerry, Hagel and Dempsey appeared to get the backing of most senators at Tuesday's hearing.
However, even proponents of military action urged Obama to do more to sell his plans to an American public that is highly skeptical after a decade of war in Iraq and Afghanistan.
Obama, who will travel from Sweden's capital to an economic summit in St. Petersburg, Russia, on Thursday, has little international support for action right now. Among major allies, only France has offered publicly to join the United States in a strike, although President Francois Hollande says he'll await Congress' decision.
Obama had canceled a one-on-one meeting in Moscow with Russian President Vladimir Putin amid tensions over Russia's granting of asylum to National Security Agency leaker Edward Snowden.
In a wide-ranging interview Tuesday with The Associated Press, Putin expressed hope that the two would have serious discussions about Syria and other issues in St. Petersburg. Putin has warned the West against taking one-sided action in Syria but also said Russia "doesn't exclude" supporting a U.N. resolution on punitive military strikes if it is proved that Damascus used poison gas on its own people.
Obama, for his part, said that he is "always hopeful" that Putin will change his position on taking action in Syria.