The Iraqi parliament just voted to expel U.S. troops from their country due to our recent political assassination within their borders. It remains to be seen if their government will approve this resolution, but I don't see why it wouldn't. The majority of Iraqis are Shia Muslims, as are nearly all Iranians. Under Saddam Hussein, the minority Sunni population was in charge — a situation that he maintained with brutal force. Once he was removed from power by GWB's disastrous war, there was nothing to keep Iran in check other than the massive presence of U.S. troops in the region.
Yes, the Sunni Islamic State (ISIS) managed to wreak havoc for a while, but Iran hadn't had time to wind its way into Iraq's halls of power and the Russians hadn't yet taken up their recently-expanded role in the region. Now, the Shiites in Iraq don't need us anymore. They have Iran to help them keep their Sunnis under control, and Iran has Russia and China to back them up. Additionally, both Iran and Russia have long been allied with the minority Shia (specifically Alawite) regime in Syria. Meanwhile, under Trump, the U.S. is closer than ever to Saudi Arabia and the other Sunni-controlled states in the region.
The next Cold War is shaping up, but instead of using communist and capitalist factions to fight proxy wars, the U.S. and Russia will square off behind Sunnis and Shiites, respectively. Israel will be officially silent to avoid angering the Arab street, but no doubt their considerable prowess in espionage and covert operations will be employed on behalf of the U.S. and Saudi Arabia.