Until recently, U.S.-Saudi relations were at their worst. Today, things differ radically, as Washington returned to regional decision-making on the basis of the bilateral relationship with Riyadh and the moderates in Tehran. Something new is coming to the Middle East that might not be a bad thing, if the leaders concerned make good decisions.
While the Iraqi military, with some help from Iran and the U.S., may be able to hold on to what is left within its purview, it's hard to see it reclaiming much territory without major foreign interventions. Which could easily backfire, both for Tehran and Washington, the only capitals which might be involved.