Rubio vows to use U.S. power to guard economic interests

By Alistair Bell WASHINGTON (Reuters) - Republican presidential candidate Marco Rubio on Wednesday urged the United States to respond aggressively when rivals such as China and Iran flex their muscles to threaten U.S. economic interests. Rubio, a U.S. senator from Florida, outlined a robust approach to world affairs at a time when China is attempting to assert greater control over the South China Sea, a vital shipping route, and Iran has threatened commercial shipping in the Strait of Hormuz. In