By asking for American help in an operation that had previously relied on Iranian planners and proxy forces, Iraq’s leaders sent a message. Either Baghdad wants the U.S. to counter Iranian influence or it has determined that Iran alone won’t cut it and American military power is needed. Or both. Whatever the reason, the outcome is that the U.S. has agreed to help, and by doing so it takes on public responsibility for the outcome. If Iraq can’t break the stalemate now, it’s an American defeat, as well. If Iraq liberates Tikrit under U.S. warplanes, and the sectarian militias really do sit the battle out, it’s an American victory.

And there could be many turns in the fighting to come. The Iranian-backed militias supposedly stepped back east of the Tigris River. But that region had long served as a staging area for fighters since the campaign began March 1. Austin also told lawmakers that Iranian forces and advisers—and presumably their weapons, tanks, and expertise—had also fled.

If that is true, the question now is whether Iran has been weakened or whether it has made a strategic retreat with the intent of reengaging after American airstrikes do the heavy lifting.