US Democratic presidential hope Barack Obama polished his national security credentials on Wednesday, introducing a Senate bill encouraging investors to cash out of projects which benefit Iran. Obama, who most national polls have in second place in the Democratic field behind Hillary Clinton, targeted Iran's lucrative oil and gas industry in a bill spurred by the US belief the Islamic Republic is building nuclear arms. The measure, also introduced in the House of Representatives by lawmakers Barney Frank and Tom Lantos, would help investors and state and local governments divest from instruments which benefit Iran. "The Iranian government uses the...