The Monkey Cage's Nolan McCarty (also of Princeton):
The stakes of the political debate [over sequestration] are heightened precisely because the extent of presidential and OMB discretion is not very transparent. For example, the president can say that the sequestration will force him to furlough air traffic controllers and Transportation Security agents, but it will be very hard to determine whether or not those cuts were inevitable. Thus, we should expect a nice round of blame-game politics where Republicans charge that [the] president has politically manipulated the cuts to make the public (especially those in bluish Republican congressional districts) feel all the pain. And the Republicans might be right, but they’ll have a tough time proving it.
We should add that if Republicans do actually attempt to prove it, to prove anything, it'll be a first. And at least that's something.