President Obama in Russia for G20 Summit: Syria Intervention Sidelines Economic Focus president obama's high-stakes challenge over syria. Facing an uphill fight with congress over a strike. He will face off with vladimir putin at the g-20 summit. Jonathan karl is traveling with the president in st. Petersburg. Good morning, jon. Reporter: Good morning, george. President obama arrived here in st. Peters, russia, just a short while ago, as vladimir putin has upped his war of words against the u.S., Accusing the obama administration of lying about syria. President obama did not come here to st. Petersburg to meet with his nemesis, vladimir putin, but to attend a summit of world leaders. But putin is the host of the summit. And the two will undoubtedly exchange a few words and a handshake or two, the first face-to-face encounter sense russia granted asylum to edward snowden. But the biggest point of contention today is syria. President obama challenged the world to support his call for a strike against syria for using chemical weapons. Noting they have been banned under international law for nearly a century. Reporter: The president said russia's efforts to block action against syria have had deadly consequences. I think that international action would be much more effectieffect i ive. And ultimately, we can end deaths much more rapidly, if russia takes a different approach to these problems. The resolution is agreed to. Reporter: The president won a narrow victory on capitol hill late wednesday, when the foreign affairs committee authorized attacking syria. John kerry urged the house to support the resolution. But he found himself under attack by president putin, whose remarks on russian television, accused him of lying about the presence of al qaeda among the syria rebels. The staff is intently focused on the debate back in washington, where a growing opposition from on ser conservatives and liberal democrats in the house, make passing that resolution authorizing force against syria, more difficult than they had thought. That begs the question of what the president would do if the relution goes down. When I talked to secretary of state kerry on sunday, he seemed to suggest that the president would strike no matter what. But that's not exactly what you're hearing. Reporter: That's right, george. The public posture remains the same. That the president retains the right, the authority to attack syria, regardless of what congress does. But the belief among his senior said aides is if congress rejects this resolution, the president would almost certainly not going forward with a military strike on syria. Raising the stakes even more. Jon karl, thanks very much.