Barack Obama promised to make shutting down the detention center at Guantanamo Bay his first mission. It turned out to be Mission Impossible, in large part because Obama never made the case for closing it to Congress or the American people. The White House will not attempt to close it by executive order, Reuters reports in an exclusive, which means that they’ve finally realized their defeat:

The Obama administration is not pursuing the use of an executive order to shutter the Guantanamo Bay military prison after officials concluded that it would not be a viable strategy, sources familiar with the deliberations said.

The conclusion, reached by administration officials, narrows the already slim chances that President Barack Obama can fulfill his pledge to close the notorious offshore prison before leaving office in January.

The White House has said repeatedly that Obama has not ruled out any options on the Guantanamo center, which has been used to house terrorism suspects since it was set up in 2001 following the Sept. 11 attacks on New York and Washington.

Ever since taking office, Congress has barred the transfers of Gitmo detainees to the US, a necessary component of shutting down the facility. The White House has routinely vowed to veto defense spending authorizations containing these riders, but the truth is that the ban on transfers has significant bipartisan support. The latest such threat prompted Mitch McConnell to ridicule Obama’s position last week as nothing more than a “stale campaign pledge” that he had no real intention of fulfilling — and no way to do so even if Obama did intend on it:

Without a path through Congress, there would be very little the White House could do to close the facility now, and almost no time in which to do it. Obama could attempt to close the entire Guantanamo Bay naval base and hand it back to Raul Castro, but that would almost certainly require Senate approval — and would create a political firestorm the likes of which have not been seen since the Panama Canal treaties of 1977. The Democrat-dominated Senate barely ratified the two treaties, with a single vote to spare on both. Obama wouldn’t be able to get any such treaty through this Senate, and attempting to try it without Senate ratification could trigger a constitutional crisis that could swamp out Democrats’ hopes in the upcoming election.

In other words, it’s all over but the shouting … and expect to hear plenty of the latter for the remainder of Obama’s term.