Former Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE says he often had to push back on President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE, telling him that some of his requests would violate the law.

“So often, the president would say here's what I want to do and here's how I want to do it and I would have to say to him, 'Mr. President, I understand what you want to do but you can't do it that way. It violates the law,' ” Tillerson said in rare public remarks in Thursday night in Houston at a fundraiser for the MD Anderson Cancer Center.

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“I'd say here's what we can do. We can go back to Congress and get this law changed. And if that's what you want to do, there's nothing wrong with that. I told him I'm ready to go up there and fight the fight, if that's what you want to do,” he added.

Tillerson said Trump would show frustration during those conversations.

Trump and Tillerson, a former Exxon Mobil CEO, were known to have a contentious relationship. Tillerson was dismissed from his post in March and replaced by then-CIA Director Mike Pompeo Michael (Mike) Richard PompeoOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Overnight Defense: House Democrats unveil stopgap spending measure to GOP opposition | Bill includes .6B for new subs | Trump issues Iran sanctions after world shrugs at US action at UN Navalny calls on Russia to return clothes he was wearing when he fell ill MORE.

The former secretary of State also said he believed Trump was able to win the presidency because the public is disengaged on many important issues.

“I will be honest with you, it troubles me that the American people seem to want to know so little about issues that they are satisfied with a 128 characters,” Tillerson said, referring to Trump's use of Twitter.

“I don't want that to come across as a criticism of him,” he added. “It's really a concern that I have about us as Americans and us as a society and us as citizens.”

Tillerson also said at the Houston event that “there’s no question” Russia interfered in the 2016 presidential election.

“What Russia wants to do is undermine our confidence and undermine the world’s confidence in us,” Tillerson said according to the Houston Chronicle.

“Many people talk about playing chess. He plays three-dimensional chess,” Tillerson added about Russian President Vladimir Putin.

Trump has repeatedly dismissed the conclusion of the intelligence community and said he accepts Putin's denials that he interfered in U.S. elections.