Iran ? Venezuela’s outspoken president joined with Iran’s leader Monday in boasting that they are “united like a single fist” in challenging American influence, saying the fall of the dollar is a sign that “the U.S. empire is coming down.”

Hugo Chavez also joked about the most serious issue the U.S. is confronting regarding Iran – nuclear weapons – during his get-together with Iranian leader Mahmoud Ahmadinejad. The visit came after a failed attempt by the firebrand duo to move OPEC away from pricing its oil in dollars.

OPEC’s weekend summit displayed the limits of their alliance – their proposal was overruled by other members, led by Saudi Arabia – but it also showed their potential for stirring up problems for the U.S. and its allies.

Making his fourth trip to Tehran in two years, Chavez has built a strong bond with Ahmadinejad that has produced a string of business agreements as well as a torrent of rhetoric presenting their two countries as an example of how smaller nations can stand up to the U.S.