There is good news and bad news in the withdrawal of President Karzai's opponent in the November 7 run-off election.
The good news is that Dr. Abdullah Abdullah will not call for a boycott of the vote. The bad news is that it probably means a cancellation of the vote and a crisis in Afghan politics.
The BBC's Andrew North reports:
President Karzai's spokesman Waheed Omar said the withdrawal was "very unfortunate", but the election should go ahead as planned.
"The process has to complete itself, the people of Afghanistan have to be given the right to vote.
Earlier, the US said a pull-out would not invalidate the vote's legitimacy.
Secretary of State Hillary Clinton told reporters in the United Arab Emirates: "We see that happen in our own country where, for whatever combination of reasons, one of the candidates decides not to go forward."
But the BBC's Andrew North, in Kabul, says Abdullah Abdullah's withdrawal means this is uncharted territory, and it is unclear what will happen next.
Asked by reporters if he was calling for his supporters to boycott the vote planned for next Saturday, Dr Abdullah said: "I have not made that call".
There has been much speculation that there could be some kind of deal which would possibly see the emergence of a national unity government, our correspondent says.
While it is far from a done deal, talks are going on behind the scenes towards such a formation.
In a sidebar to the story, North writes:
It is almost certain the second round vote planned for 7 November won't happen.
Instead, pressure is mounting on the Afghan election commission to call it off and for the Supreme Court to issue a ruling declaring President Karzai the winner.
Despite calls by some of his supporters for the vote to go ahead, his campaign has now said it will respect any decision by the commission and other legal institutions.
Much of the pressure has been coming from foreign diplomats - the same diplomats in many cases who insisted on a second round to try to restore some legitimacy to the process because of the widespread fraud first time round.
But the United Nations as well as the British, American and other governments with troops here are not prepared to risk their lives for a one-man race.
It will be a deeply unsatisfactory end to the process but at the moment this is seen as the best option. Then will come the decisions on a new Afghan government.
Obama may very well use this confusion as an excuse not to announce his Afghanistan strategy until after some kind of government emerges from the ongoing talks. The way the negotiations seem to be heading, that might not be for weeks.
How much more patience can Obama ask of the American people in formulating his new Afghanistan strategy? With his own supporters already agitating for a decision, it won't be very long at all before the president's dithering will be seen as incompetent indecision on what to do. And circumstances elsewhere - including the slow pace of health care reform and a lack of progress on bringing unemployment down - may make Obama a figure of derision rather than a messiah.