When US President Donald Trump received Iraqi Prime Minister Haider Al-Abadi in the Oval Office last month, he assured the Iraqi leader that the US would support the war-battered country “in our shared fight against” the Islamic State (IS) terrorist group. “The United States and Iraq stand fully committed to a comprehensive partnership, rooted in mutual respect and grounded in the United States-Iraq Strategic Framework Agreement, which provides a framework for political, economic, cultural and security cooperation,” Trump told Al-Abadi. Al-Abadi, one of the first foreign leaders Trump hosted at the White House after he became US president, returned to Baghdad in an upbeat mood after a warm reception by Trump and his promises for “greater support” for Iraq in battling terrorism. Trump's assurances were also seen as a personal commitment to work together with Al-Abadi's government after remarks he had made during his election campaign that he might re-invade Iraq and take its oil. But Al-Abadi's celebration soon gave way to a gloomy atmosphere in Baghdad after Trump's bombing of Syria last week. Now Iraqi Shia leaders fear that the US engagement in Syria may undermine their efforts to defeat IS in Iraq. Trump ordered missile strikes on a Syrian airbase last week in reprisal for a deadly chemical weapons attack Washington claimed had been carried out by the regime led by Syrian President Bashar Al-Assad. The bombing was a stark reversal from Trump's formerly stand-off approach to the six-year old civil war in Syria and his administration's policy of focusing on “America first” and opposing intervention elsewhere in the world. Trump justified the strikes as being in the “vital national security interest of the US to prevent and deter the spread and use of deadly chemical weapons”. But the military and political case for the bombing remains controversial. Iraq, among all Syria's neighbours, is expected to be the worst impacted by the regional fallout of the military escalation, though this will depend on how events unfold. The Iraqi government's initial response was carefully calculated. A spokesman for the Foreign Ministry voiced concerns that “the interventions and the hasty measures could negatively impact efforts to fight terrorism.” The Iraqi reaction was also softened by Al-Abadi himself, who condemned the chemical weapons attack in Syria and suggested that there be an “urgent international investigation” into the use of chemical weapons in Syria in order to deescalate the crisis. Shia political groups in Iraq, however, reacted sharply and accused the Trump administration of trying to “embolden terrorist groups”. Powerful Shia cleric Muqtada Al-Sadr described the bombing as “reckless.” “He [Trump] should not jump into new carnage which everyone will pay for,” he said in a statement. Some militia leaders went as far as to accuse Trump of trying to align the US with Saudi Arabia and other Sunni Arab governments in order to “target the opposition trend,” a reference to pro-Iran groups in the Middle East. Like Iraq, Syria is a religious and cultural mosaic, and the conflict in Syria could lead to further ethnic and sectarian polarisation in Iraq, with different groups vying for power and shares in the country's wealth. Trump administration officials insisted that the 7 April strikes were only meant to convey the message that chemical weapons were “unacceptable” and that the administration's overall policy on Syria had not changed. Just a few days before it launched the strikes, the Trump administration signalled a willingness to let Al-Assad stay in power, suggesting that his “longer-term status” will be “decided by the Syrian people”. Given Trump's notorious unpredictability, it is not clear exactly what the US administration seeks to achieve in Syria following the air strikes. Yet, there are increasing fears that there might be “mission creep,” especially because of the presence of hundreds of US soldiers in northern Syria helping Kurdish fighters prepare to assault the IS stronghold of Raqqa. What may happen next is a cause of worry to Iraqi Shia leaders in view of the uncertainties surrounding Trump's Middle East strategy and the possibility of a wider conflagration. Many Iraqis believe that a wider escalation in Syria will open the door to further risks of wild and contradictory conflicts that would not only engulf Iraq and Syria but also the entire region. Turkey and US Sunni Arab allies in the Gulf opposed to Al-Assad have lauded the strikes, which they hope will help to increase the pressure on the Syrian regime and eventually topple it and replace it with a more friendly one. The regional Sunni alliance also has high expectations that a new hardline US strategy vis-à-vis Syria could help to contain Iran and its Shia allies in Iraq, Lebanon and Yemen. Hours after the US navy shelled the airbase in Syria with cruise missiles, king Abdullah of Jordan warned of what he termed “Iran's strategic intent to have power” in the region. “There is an attempt to forge a geographical link between Iran, Iraq, Syria and Hizbullah/Lebanon,” the monarch told the US newspaper the Washington Post in an interview. King Abdullah, who has coined the term “Shia crescent” to refer to Iran's influence in Iraq, Lebanon and Syria, is widely seen as a key partner in Trump's strategy in Syria, including establishing safe zones inside Syria that could be used as lynchpins for opposition groups to topple Al-Assad. Iraq, which shares a 375 mile (600 km) border with Syria, has repeatedly cautioned that the crisis in Syria could spill over into its territory if serious efforts are not made to stop the violence and promote a political settlement. The Iraqi Shia-led government's most immediate fear is that Trump's priority will now be to challenge Al-Assad and probably to take on his regime instead of destroying IS as he boasted during his election campaign. With the Trump administration changing its policy direction on Syria, the Iraqi Shia leadership fears that the regional Sunni bloc will throw its weight behind Al-Assad's Sunni opponents who are armed and financed by regional Sunni powerhouses such as Qatar, Saudi Arabia and Turkey. The collapse of Al-Assad's Alawite-dominated regime could put Syria's Arab Sunni majority in power in Iraq's Western neighbour and embolden Iraqi Sunnis, thus increasing the challenge to Shia control in Iraq. The Iraqi Shia leaders also fear that increasing US involvement in the civil war in Syria could leave Washington in union with Turkey and the Sunni nations in the Gulf that are opposed to the close ties they have forged with Iran, Al-Assad's key backer. On 6 April the Saudi-owned Al-Hayat newspaper disclosed what it described as Trump's strategy in Syria which aimed primarily at “weakening the Shia crescent” extending from Iran to the Mediterranean through Iraq. Quoting unnamed “Western officials,” the paper said Trump's plan included a US military build-up in western Syria, including outposts and airstrips that will function as barriers against the Iranian influence coming through Iraq. The report coincides with the disclosure that Trump's strategy in Iraq will require a re-direction by Al-Abadi of his government's positions on several key issues, among them the role of Iran. It will also require Arab Sunni governments to work to entice Baghdad away from Tehran. Saudi Arabia has already started warming up relations with Al-Abadi's government, ending a diplomatic crisis after Riyadh accused Iraq's Popular Mobilisation Forces (PMF) of being a “sectarian militia organisation” with affiliations to Iran. What may worry Iraqi Shia leaders is that the new US approach towards Iraq and Syria could be even more polarising and push Iraq further into instability and probably fragmentation. On Monday, a statement from a so-called Military Operations Room of Russia, Iran and Hizbullah in Syria accused the United States of “supporting schemes which aim at dividing Syria and Iraq”. The statement by the main Al-Assad backers threatened that their forces under joint command would retaliate against any further US “aggression” against Syria. Such avowed support for its ally Al-Assad would have riled the Iraqi Shia leadership at any time. But it is particularly unwelcome at this juncture, for the Shia-led government in Baghdad is in dire need of US help in its war against IS while it is absorbed by a Kurdish separatist drive and Iraqi Sunni demands for greater inclusion. As Iraq remains caught in the middle of the regional struggles, its plight in this vicious circle of conflict in its neighbourhood is expected to be dire and worsening.