ST. PETERSBURG, Russia (AP) — President Barack Obama says he understand the American public's deep skepticism about launching military action against Syria. But he says he is confident he can persuade Americans that the use of chemical weapons in Syria requires a military response. Obama says he needs to convince the nation that his plans would be "limited and proportional" and designed to uphold international norms. Obama says a chemical attack in Syria last month was carried out by President Bashar Assad's military. Seeking congressional authority to act, Obama says the U.S. experience with Iraq and a decade of war has made the public wary, especially within his own Democratic Party. He says, quote, "I trust my constituents want me to offer my best judgment. That's why they elected me. That's why they re-elected me."