St. Petersburg, Russia — President Barack Obama on Wednesday declared the world’s credibility “is on the line” when it comes to punishing Syrian President Bashar Assad for his regime’s purported use of chemical weapons. Speaking at a press conference in Stockholm, Sweden, ahead of a global economic summit in Russia where he will seek to rally support for a U.S. military strike against Syria, Obama said the “red line” he set against a year ago against Syria’s use of chemical weapons isn’t his, but an international standard. “I didn’t set a red line, the world set a red line,” Obama...