The United Arab Emirates and the United States enjoy very close strategic ties. The UAE has been described as the United States' best counter-terrorism ally in the Gulf by Richard A. Clarke, the US national security advisor and counter-terrorism expert. The US maintains three military bases in the UAE. The UAE is also the only country in the Middle East which has a US border preclearance that is staffed and operated by US Customs and Border Protection officers, allowing travelers to reach the US as domestic travelers. In 2013, The UAE spent more than any other country in the world to influence U.S. policy and shape domestic debate. In its dispute with the United States, Iran has repeatedly threatened to close the Strait of Hormuz, a vital oil-trade route. Therefore, in July 2012, the UAE began operating a key overland oil pipeline, the Habshan–Fujairah oil pipeline, which bypasses the Strait of Hormuz in order to mitigate any consequences of an Iranian shut-off.