The United States’ Secretary of State Rex Tillerson may be considering parting ways with the White House amid widening differences with President Donald Trump on a number of subjects, including on Iran, US sources say.

The CNN reported on Monday that Tillerson faced “a growing list of differences with the White House, including a new debate over Iran policy and personnel.”

A former CEO at the oil and gas giant ExxonMobil, Tillerson was appointed secretary of state after Trump secured an upset victory in the US presidential election in November last year. As America’s top diplomat, Tillerson would have been expected to play a considerable role in policy-making and have the president’s ear on foreign policy in particular.

Frustration at boiling point?

But since assuming office in January this year, Tillerson has seen room shrinking for him in the president’s inner circle. On a number of major issues, he has either been sidelined, overruled, rebuked, or ignored altogether.

However, he had been hoping that the status quo would change for the better.

Until now, that is.

Two sources “familiar with Tillerson[’s] conversations with friends outside Washington” told CNN that the US secretary of state was growing increasingly frustrated and was losing hope that a shift in the presidential mood was in order.

While he had previously signaled determination to stay at the job for at least one year amid the differences, the sources said “they would not be surprised if there was a ‘Rexit’ from Foggy Bottom sooner that [sic] that.”

Tillerson’s differences with the White House first emerged when the administration proposed to drastically slash State Department funding in May. In a leaked internal State Department memo, Tillerson said he was “deeply concerned about the timing and the size of the reductions.” He did not get his way, and ultimately offered a public defense of the cuts, a sign that he was unwilling to let the matter turn into an open dispute.

According to the CNN, Tillerson was also opposed to Trump’s recent public reprimand of Attorney General Jeff Sessions over the latter’s recusal from an investigation of White House links with Russia.

Most recently, Tillerson was said to have been rebuked by Trump because the secretary of state had failed to provide the US president with “options” other than certifying Iranian compliance with a 2015 multilateral nuclear deal, to which the US is a party.

Trump has reportedly assigned a team of White House confidantes to look for ways to avoid a recertification in the future, sidelining the State Department.

Tillerson has not publicly clashed with Trump, and his personal views regarding Iran are largely unknown. He recommended recertification of Iranian compliance in a recent meeting of Trump’s national security team, but has not conspicuously strayed from the hard-line stance of the Trump administration vis-à-vis the Islamic Republic.