NYT:

[T]he senior administration official said there was some debate within the administration about how openly to question the result. While some political operatives in the administration wanted to be more open about American unease with the election result, those from diplomatic backgrounds were portrayed as pressing for the United States to say as little as possible, so as not to disrupt the engagement process, which Mr. Obama has made one of his foreign policy priorities.

Something to keep in mind here is that many Iranians still resent the CIA's role in a 1953 coup that overthrew Iranian Prime Minister Mohammad Mosaddeq and installed the Shah, and America's long support for the Shah's brutal and corrupt regime. If Mousavi was indeed the rightful winner here, then it's obviously a very different situation from an unpopular coup. But it's still understandable that some in the Obama team might want to be very careful about appearing to meddle in internal Iranian politics. (Obama conceded America's role in the coup in his Cairo address; Madeleine Albright did the same in 1999.) 

Meanwhile, NPR is reporting that the demonstrations in Tehran have largely subsided, although MSNBC says a large protest march is planned underway.

--Michael Crowley