The two nations were bitter rivals for decades when Saddam Hussein's Sunni dominated regime was at war with Tehran's Shiite-led government. After the U.S. invasion, the Iraqi government came to be dominated by Shiite leaders, who now finds themselves under assault from the Sunni militants of ISIS. Now Iran sees Baghdad as a strategic partner, and the ISIS militias as unacceptable neighbors.
Meanwhile, the United States has been noncommittal about how much it is willing to offer. In a statement on Thursday, PresidentObama said, "I don't rule out anything," but the White House appears reluctant to risk any military assets that might draw the Americans back into a war they just got out of. Obama said the government in Iraq is going to need more help, but expressly stated that ground troops are not an option.
However, if Iran is willing to do more than the U.S. to protect the people in Baghdad in the immediate future, then the list bad options in the region could soon get much worse.