The killing of top Iranian general Qassem Suleimani a year ago placed a heavy strain on relations between Iraq and the US.
But as president-elect Joe Biden prepares to take office next month there is room for improvement, experts said.
Suleimani was killed alongside top Iraqi militia leader Abu Mahdi Al Muhandis by a US air strike at Baghdad airport on January 3. This gave renewed impetus to Iranian allies in Iraq, raising the spectre of civil strife in a country torn by years of sectarian conflict
"There is mistrust between both sides, the US feels that Iraqi political leaders are not doing enough to protect its troops and diplomatic missions in the country and accusing some sides of conducting these attacks," Sajad Jiyad, a Baghdad-based fellow with the Century Foundation, told The National.
Washington breached Baghdad’s sovereignty by killing a senior official without permission, Mr Jiyad said. “There is still mistrust between them.”
The US embassy in Baghdad, as well as American troops stationed around the country, have faced dozens of attacks since then, seen as part of an extended response to the killing.
The relationship between the two, and the US presence in the country, is based on an agreement signed in 2008. It called for close defence co-operation to deter threats to Iraqi “sovereignty, security and territorial integrity".
In 2011, Washington withdrew its forces from Iraq, eight years after leading the invasion that toppled dictator Saddam Hussein and set off a bitter sectarian conflict.
Thousands of American soldiers were redeployed to the country from 2014 onwards as part of a coalition battling ISIS.
A year of tensions - in pictures
Ties between Baghdad and Washington were tense, in what became known as post-ISIS Iraq. The question looming was “to which extent was the US going to use Iraq as a battleground for regional politics, in particular with Iran”, said Renad Mansour, senior research fellow and Iraq expert at Chatham House.
In recent years, especially after President Donald Trump assumed office in 2016, Iraq has been vital to Washington’s strategy of containing the expansion and power of the Iranian regime.
The Trump administration’s “maximum pressure” campaign on Iran weakened its economy but did not stop Tehran from pushing its agenda in the region, including supporting its proxies in Yemen and Syria.
"It put Iraq in the line of fire," Mr Mansour told The National.
"Baghdad felt stuck between its powerful neighbour – which it could not alienate – and the US, the most powerful external actor [apart from] Iran,” he said.
“It strained Baghdad-Washington relations."
Shortly after the attack Iraq’s parliament voted for the departure of foreign troops from Iraq, and the US and other coalition troops have been leaving as part of a drawdown.
Looking ahead
With the new administration to take office in January, experts say the US will not increase its engagement with Iraq to the level it once was.
“I believe 2021 will be a different year for US-Iraqi relations, the change of administration in Washington will have a big effect on that,” said Abbas Kadhim, director of the Iraq initiative at the Atlantic Council.
There will be an increase in diplomatic co-operation between the two. Baghdad will receive less demands and threats from Washington, he said.
Political leaders in Baghdad face many challenges and would need to figure a way to sort out the country's internal issues, and to determine what kind of relationship it would have with Washington.
“The government needs to sort out the relations with political and non-state actors, who are using arms and not showing strong co-ordination with the commander in chief, while getting its act together economically, financially, and politically,” Mr Abbas said.
Mr Biden’s administration will clarify what the US wants from Iraq and vice versa.
“There will be a change with Biden, which will be more positive going forward. The potential to improve ties is there but 2020 has been a difficult year,” Mr Jiyad said.
Leaders in Baghdad are "optimistic that relations will improve with Biden with the support he has promised with the economic crisis and reducing tensions with Iran," he said.
