A US civilian contractor was killed and several US service members and Iraqi personnel were wounded in a rocket attack on the K1 base near Kirkuk on Friday night.It is the most serious escalation in a series of rocket attacks that have targeted bases in Iraq where American and US-led coalition troops are present.Since May there have been at least a dozen of these attacks. Some wounded Iraqi security forces, but US forces had not suffered casualties before.President Donald Trump must decide to respond, as the US has threatened to do.The rocket attack comes amid a political crisis in Iraq where the prime minister has resigned and the president has threatened to quit. Demonstrations have swept the country for three months and Iranian-backed forces are accused of killing up to 500 protesters in Iraq. At the same time Iraq is a center for Iranian entrenchment and weapons transfers that threaten Israel.Any US response will have a regional impact that can affect Syria , Israel and the Gulf.The first issue facing the administration is to decide who is responsible. It is either the Islamic State or a group linked to Iran.Reports indicated that Iraqi Federal Police had located the rocket launcher and found four rockets intact.The widespread assessment is that ISIS doesn’t have the capability to fire many rockets. It hasn’t conducted rocket attacks recently. The terrorist group has been increasing its activity around the areas of Kirkuk and Diyala and has networks operating in caves and streams linking Kirkuk to Hawija, the Hamrin Mountains and up toward Makhmour, and west toward the desert.James LaPorta of Newsweek reported that US intelligence officials said they believe Iranian-backed militias were the culprit.Lucas Tomlinson at Fox News reported that sources said around 30 rockets landed at the base. “This is the 11th rocket attack on US and Iraqi forces since late October, according to a US defense official.”Reuters claimed the US was looking into the possibility that Kataib Hezbollah was behind the attack. Security forces of the Federal Police found a “launchpad for Katyusha rockets inside an abandoned vehicle near the base.” There is confusion about the overall number of rockets fired and what happened. Initial reports said more than 10 rockets were fired and that a munitions storage facility was struck, causing it to blow up. But then estimates said the overall number of rockets fired was more than 30, as many as 36, and that at least four intact rockets were found. It’s thought a Bongo-style truck with rockets mounted on the back was used.As the investigation unfolds, Trump will be reminded that Secretary of State Mike Pompeo has warned Iran repeatedly against attacks on the US in Iraq. In mid-December, Pompeo said the US was reminding Iran’s leaders that “any attacks by them, or their proxies, of any identity, that harm Americans, our allies, or our interests will be answered with a decisive US response.”On December 6, David Schenker, assistant secretary of state for Near Eastern affairs at the US State Department, indicated that Iran could be behind the attack on Iraq’s Balad air base. In that attack two Katyusha rockets landed inside Balad air base north of Baghdad. “We’re waiting for full evidence, but if past is prologue then there’s a good chance that Iran was behind it.”A US military official went further on December 12, telling National Public Radio that a rocket attack by four Katyusha rockets near Baghdad Airport was part of a broader trend of attacks on US and coalition positions. He said these included a November 8 attack on Qayyarah West base with 107 mm. rockets fired from a truck. Then came a December 3 attack from a truck using 122 mm. rockets aimed at Al-Asad base.The official then referenced 240 mm. rockets being fired near a US compound in mid-December. Those were Iranian-made rockets. The US pointed a finger at Kataib Hezbollah at the time. These larger rockets were first used against US forces in 2007, also by pro-Iranian groups in Iraq.On December 17 US Central Command said the US had made clear that attacks would not be tolerated. Throughout the attacks the US has relied on Iraqi forces to investigate. Those forces have sometimes found the trucks linked to the attacks. As far back as February and May, rocket launchers aimed at US bases had been found, but those reports were largely ignored at the time. The pattern of attacks has grown so intense that it now led to casualties.If the US determines that pro-Iranian groups were behind the recent attack it will have to decide how to respond. The US sanctioned Qais Khazali, head of the Iraqi Shi’ite paramilitary group Asaib Ahl al-Haq, on December 6. Khazali’s group is one of many in the Popular Mobilization Units, a paramilitary unit made up of mostly Shi’ite militias. Many of these groups have close links to the Islamic Revolutionary Guard Corps. This includes Badr, which has the largest number of PMU brigades, Kataib Hezbollah, Harakat Hezbollah al-Nujaba and Asaib Ahl al-Haq.Kataib Hezbollah is run by Abu Mahdi al-Muhandis, the PMU’s deputy and a US-designated terrorist. Muhandis has threatened US troops in the past. He has also said the PMU needs an air force and has pointed a finger at the US and Israel for attacks on Kataib Hezbollah bases in the past. In August he said the US and Israel had conspired to attack PMU munitions warehouses after four blasts destroyed PMU storage facilities in July and August. US officials expressed concern about tensions with Israel in Iraq and Syria after the incidents. Kataib Hezbollah also had a base near Albukamal in Syria on Iraq’s border. That headquarters was destroyed in an airstrike in June 2018.Last week IDF Chief of Staff Lt.-Gen Aviv Kochavi indicated Israel opposed Iranian entrenchment in Iraq. Iran has been alleged to be transporting ballistic missiles to Iraq since August 2018. On December 4 reports said intelligence agencies had been tracking new Iranian shipments of ballistic missiles to Iraq.In addition Iraq is in the midst of a political crisis. The prime minister has resigned and the president has threatened to resign after almost three months of protests. Five hundred Iraqis have been killed and 19,000 wounded. The pro-Iranian militias, like Asaib Ahl al-Haq and Saray Khorasani, are blamed for killing protesters. Iran wants to push a pro-Iranian candidate for prime minister. This means that the rocket attack comes at a key moment in Iraqi history.Iraqi President Barham Salih has been condemned by Asaib Ahl al-Haq for being seen as too close to the US. Pompeo met Iraqi leaders in January and then in May when he warned of Iranian threats. He also met Salih in September on the sidelines of the UN.Iraq could be seen as a key place of struggle between the US and Iran. However US forces are in Iraq at the invitation of the government to help fight ISIS. There is no mandate to also fight Iran. Iraqi politicians were angered when Trump said in comments in December 2018 and January 2019 that the US could use Iraq to “watch” Iran.While the rocket attack near Kirkuk could lead to a US-Iran crisis, Iran is holding naval drills with Russia and China and claiming that US hegemony is weakening. Iran has already attacked oil tankers in the Gulf of Oman and downed a US drone. It also attacked Saudi Arabia in September. It has launched at least four rocket attacks on Israel from near the Golan, in May 2018 and in January, September and November 2019. In this context the next move that Trump chooses in Iraq has implications across the Middle East.