Pro-Iranian groups in Iraq are leading efforts to oust American military forces from the country.The campaign is gaining strength following the American airstrike at Baghdad's airport last Friday.That attack killed Iranian General Qassem Soleimani and Iraqi militia leaders.In a vote Sunday, Iraqi lawmakers called on the governmentto remove the 5,200 American troops now in the country.The path forward is unclear and observers are warningthat ending the United States' 17-year military presence in Iraq carries risks.Iraqis were starting to recover from a four-year war against the Islamic State (IS) groupwhen mass protests against the country's rulers began October 1.The unrest led to the resignation of Prime Minister Adel Abdul-Mahdi two months later.However, a replacement has not been made and Abdul-Mahdi remains in office.An American troop withdrawal could affect the fight against IS militants and enable them to make a comeback.Fighters allied with the group often carry out attacks in northern and western Iraq.Iraqi forces depend on the U.S. military for weapons and equipment in their operations against them.An American withdrawal could also enable Iran to deepen its influence in Iraq,which like Iran, is a majority Shiite country.Ibrahim Bayram, a political observer from Lebanon, said a withdrawalwill, "increase the complications inside Iraq, the conflicts and contradictions ...and the clash, both political and non-political, between the Iranians and Americans."The vote in parliament on Sunday requires Iraqi government approval to remove the American troops.It is evidence of the worsening in relations between the countries,at a time of rising tensions between the United States and Iran.U.S. forces withdrew from Iraq in 2011 but returned in 2014at the invitation of the government to help battle the Islamic State group.The extremists had seized large areas in the north and west of the country after Iraq's armed forces collapsed.A U.S.-led coalition provided air support as Iraqi forces, including Iran-supported militias,regrouped and drove IS out in a costly three-year campaign.Following the defeat of IS in 2017, pressure grew,especially among groups loyal to Iran, for the withdrawal of U.S. forces.The U.S. airstrike last week at Baghdad's airport fueled anger.Abdul-Mahdi asked parliament on Sunday to take "urgent measures"to ensure the removal of foreign forces from the country.Many Sunni and Kurdish legislators boycotted the parliament meeting.They oppose cancelling the deal with the Americans.Most of the lawmakers who voted were Shiite Muslims.On Monday, Abdul-Mahdi met with U.S. Ambassador Matthew Tueller.A statement from the prime minister's office noted the need for the two sides"to work together to execute the withdrawal of foreign troops from Iraq."In their meeting, Abdul-Mahdi said the situation in Iraq was "critical"and that all efforts were being taken to prevent "an open war."The Iraqi parliament vote angered U.S. President Donald Trump,who warned Iraq that he would take action if the government expelled American troops.He said the U.S. would not leave without being paidfor its military investments in Iraq over the years."We will charge them sanctions like they've never seen before, ever.It'll make Iranian sanctions look somewhat tame," Trump said.