Confronting ISIL in Iraq now depends largely upon the stance taken by Iran. According to recent reports Iran had expressed its willingness to help stop the advance of ISIL and decided to send an entire fleet of fighter jets to Iraq. Needless to say, Iraq isn't capable of handling the situation on its own. The $20 billion training imparted to Iraqi forces by the US was only on torture techniques, not combat skills. Iraq's dependency on the US would only make it weaker at the hands of ISIL.
United States' support for Shiia Iraq was on the rebound following the fall of Saddam. But that's water under the bridge. The story is altogether different at the moment. The United States (and Israel) now sees Iraq as Iran's ally. Consequently it has also acquired a partner of convenience within the various Salafist camps that are sworn enemies of Iran, Iraq and Syria. The need for promoting Zionist hegemony in the Middle-East has never been more for which Iran and Syria are seen as formidable obstacles. As it would be simple enough to gauge, United States is no longer interested in pampering the immediate successors of Saddam whom it brought into power after toppling the Baathists a decade ago.
With the Syrian Army and Hezbollah taking care of Levant and its borders with Iraq, now is the time for Iran to act jointly with Iraq. Otherwise there is a huge possibility that optimism could be lost sooner rather than later.