And on Monday, Sen. Bob Corker stood by those remarks, adding: "My thoughts were well thought out."
"Look, I didn't just blurt them out," Corker, a Tennessee Republican, told CNN. "My comments -- my comments, I stand by them -- yes."
Corker also added a fresh complication to the intensifying White House push to overhaul the tax code, saying that he would oppose any tax-cut bill that would raise the deficit.
"No," Corker said when asked if he would back a tax plan that would hike the deficit. "I mean, I've stated that clearly."
Last week, Corker offered the sharpest criticism of Trump of any Republican senator to date, questioning the President's actions, tweets and temperament, telling The New York Times
that his concerns were shared by nearly every member of the 52-person Senate GOP Conference.
It amounted to a stunning rebuke by the powerful chairman of the Senate foreign relations committee, whom the President contended was retiring next year because Corker could not win his endorsement. Corker flatly denied that was the case.
"Look I've been expressing concerns for some time and it's built over time," Corker said Monday. "I've had private dinners, I've had private phone calls, I've tried to intervene on topics that I thought things were going in a different direction and are not going to be good for our country. This is not a new thing, it's been building for some time. And it's a pattern that I think we've fought and expressed for some period of time."
Behind the scenes, some members of Trump's administration seemed to be trying to make amends
with Corker since the flap last week. Vice President Mike Pence called Corker, a sign that he is reprising his role as a peacemaker in the administration.
Corker also said he spoke with Steven Mnuchin, the Treasury secretary, about tax reform issues, as well as Secretary of State Rex Tillerson, whom Corker previously said was part of a trio of senior administration officials preventing the United States from descending into "chaos."
"I've had (conversations) up-and-down from Pence, to our Treasury Secretary Mnuchin to Tillerson to just like we always do," Corker said of his conversations over the past week.
Despite the flap, Trump needs Corker -- who is chairman of the foreign relations committee -- to help usher through new legislation on the Iran nuclear accord, after the President asked Congress to find a new solution on the matter within the next two months. In order to win over support in Congress, particularly from Democrats, Corker contended that the Trump administration needs to allay fears from Europe that the legislation would not blow up the nuclear accord with Iran.
"It is something that can only work if the administration exercises tremendous diplomacy with our European allies," Corker said.
And Trump also needs Corker's vote to help pass a major tax reform proposal, something that faces an uphill climb in the Senate given the narrow majority Republicans hold.
"I'm very concerned as everyone knows and have been for 10 years and nine months since I've been here about our deficits," Corker said. "And I want to make sure that it's not something that increases deficits, and I also want it to be tax reform."