Tillerson initially gave a lengthy answer defending Trump as an "unconventional President" who is clashing with a Washington afraid of change and hard decisions.
"You can not publicly castrate your own secretary of state", Corker, the chairman of the Senate Foreign Relations Committee, told The Washington Post.
The US ambassador to the United Nations Nikki Haley pushed the same argument during appearances on Sunday talk shows, telling ABC's This Week that reevaluating the Iran deal "sends the flawless message to North Korea, which is, we're not going to engage in a bad deal".
Trump also grew annoyed with what he perceived as Tillerson's go-it-alone approach to diplomacy with North Korea, declaring in a scorching recent tweet that the secretary of state was "wasting his time trying to negotiate with Little Rocket Man", Trump's nickname for Kim Jong Un.
Ireland Fall In World Rankings After Rugby Championship Results At The Weekend
The coach said the hard work was starting to pay off for the team: "The players are enjoying playing for the Springboks", he said. The All Blacks, ranked one in the world, won the Rugby Championship with 28 from a possible 30 points.
He doubled down on his support for the secretary of state Friday, saying that while he was concerned about Trump's "very irresponsible" Twitter habits, "it's the first part" - the "castration" of Tillerson - "that I am most exercised about".
Senator Corker made the claim in a Washington Post interview last week amid a public spat with the president. "How he wants to use his own skills tactically to push things toward change, I am there to help him achieve those".
It was unclear why Tillerson was unwilling to repeat what his spokeswoman has said on his behalf. Tillerson, meanwhile, is said to have grown tired of Trump contradicting his public pronouncements and of becoming increasingly isolated in a capital to which he has never warmed. "And so everything that I have witnessed, all was fine", she said.
Signs of tensions between Trump and Tillerson have raised questions among in foreign capitals about whether the secretary of state speaks for the administration.