The withdrawal of Afghan presidential challenger Abdullah Abdullah ends the electoral stalemate that has split the country for more than two months.
Former Prime Minister Abdullah backed out of a Saturday runoff against President Hamid Karzai. The runoff became necessary when Mr. Karzai failed to garner the majority vote necessary to win the August election after international inspectors rejected more than 1 million Karzai votes due to fraud.
Mr. Abdullah doubted another election conducted by the country's same election infrastructure could conduct an independent and transparent runoff vote. He had demanded the removal of some members of the election commission, but that was rejected by Mr. Karzai.
Mr. Abdullah's decision made it possible Monday for the commission to cancel the runoff and declare President Karzai re-elected to a five-year term.
Mr. Abdullah's decision is a blow to the Obama administration, which had been hoping the runoff election would yield a clear winner with the legitimacy needed to run the country in the coming years.
President Karzai's re-election was overshadowed by claims of fraud that could make it difficult for the administration to continue U.S. support of a corrupt government at the risk of more American lives.
But senior Obama adviser David Axelrod said Sunday that the White House expected President Karzai to win. After the commission's decision, the administration signaled its support for President Karzai, even though he has been criticized for a high degree of corruption.
Mr. Karzai had also criticized U.S. military tactics, especially the use of air power to strike at militants in his country.
U.S. efforts to negotiate a power-sharing deal between the two candidates fell through, but officials expressed hope that President Karzai may yet include Mr. Abdullah or his followers in the government, a move that might help reconcile factions within Afghanistan.
Afghanistan needs a government that can unify the country.