Story highlights Tillerson questioned Trump's intelligence to other top officials

The episode prompted deep frustration from the President

Washington (CNN) Secretary of State Rex Tillerson, the stone-faced former oil executive Donald Trump tapped to serve as his global envoy, is increasingly seen by administration officials and diplomats as on his way out -- just as flash-points from Iran to North Korea flare.

The impression that Tillerson's days as Trump's top diplomat are numbered was fueled this week by new reports of acrimony between the two men -- principally, that Tillerson had questioned Trump's intelligence to other top officials.

The episode prompted deep frustration from the President, who fumed that a supposed underling was insulting him to his cohorts. And it only seemed to cement his impression of Tillerson as a reluctant participant in Trump's foreign policy agenda, areas of which the two men have had public disagreements about.

More than a dozen sources inside the administration and in diplomatic circles describe the relationship between Tillerson and Trump as reaching a new low. The two men have failed to develop the type of close relationship that Trump enjoys with other members of his Cabinet. Radically different in personality, Tillerson and Trump have chafed at each other's perceived slights.

Tillerson has told friends he intends to remain in his post for at least a year, a psychological deadline that would allow him -- in his own mind -- to depart with dignity. But irritation with his boss, paired with frustration at the entrenched ways of Washington, have led him to waver at times.

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