Lebanon holds parliamentary elections June 7. Analysts predict the March 8 coalition, which includes Hezbollah, may take a slim majority over the pro-Western March 14 slate.
While the United States would not sever diplomatic ties with Lebanon, relations would scale back in the event of a March 8 victory.
A March 8 victory would bring the opposition to power, though the Shiite Hezbollah would not rule in the majority. With the Lebanese government mandating a Sunni prime minister, meanwhile, it would be "very difficult" to form a government led by the opposition, says Michael Young with the Lebanese Daily Star.
With a March 8 victory, many in the March 14 camp, including Saad Hariri, the Sunni head of March 14 and son of slain former Prime Minister Rafik Hariri, said they would boycott the government, leaving Beirut in shambles.
"If the opposition wins, Lebanon will indeed enter into a period of long instability," Young warns in an interview with the Council on Foreign Relations.
He said the best outcome would be a modest victory for March 14 that would still bring the opposition into a unity government.
With U.S. Vice President Joe Biden and Secretary of State Hillary Clinton making high-profile visits to Beirut, Young says the message from Washington is abundantly clear.
"If Lebanon votes right, as they see it, then there would be advantages to Lebanon," he said.