Vice President Biden delivered a clear message to Iran, saying Saturday the U.S. was willing to talk, but will act to isolate and pressure Tehran if it does not abandon its nuclear ambitions and support for terrorism. In a sweeping speech to international leaders and security experts here, Biden said the U.S. will strive to act preventively to avoid having to choose between the risks of war and the dangers of inaction. But he held out the option that the U.S. could take pre-emptive action against Iran if necessary to stop crisis before they start. The U.S., he said, will...