Tens of thousands have rallied in favor of Ahmadinejad challenger Mousavi ahead of June 12 election.
Secretary of State Hillary Clinton meets Wednesday with the Millenium Challenge Corporation to decide whether to cancel US aid in response to the leftist leader's alleged attempts to steal elections.
The Western-backed March 14 coalition won an unexpectedly large parliamentary majority – 71 of 128 seats – over the opposition, led by the Iranian-backed militant group.
Mahmoud Ahmadinejad faces a surge from the more moderate challenger Mir Hossein Mousavi, as more educated urban voters tire of his polarizing politics.
A Hezbollah victory would strain ties with the US and with pro-Western nations like Egypt, Jordan, and Saudi Arabia.
The American president took his case straight to the people on his trip this week, spending limited time with the leaders of Saudi Arabia, Egypt, Germany, and France.