"That is the No. 1 job of the chief executive of the United States," he said. "And that's not an easy job."
The health of the economy at the end of four years is a second yardstick by which Buffett said he'd evaluate the Republican Trump administration.
"And then third, I'll judge him on if the economy does well, which I expected it to do, how wide the participation in a better economy extends."
Reminding investors of his past statements, Buffett pointed out that he said the U.S. economy would be fine under Clinton or Trump.
To that end, Buffett told CNBC on Monday that mixing politics and investment strategies would be a "big mistake."
"Probably half the time [in] my adult life, I've had a president other than the one I voted for," he said. "But that's never taken me out of stocks."
"Tillerson makes a lot of sense," he said. "Tillerson is going to be working for the United States in that job."
"I don't worry at all about whether somebody comes from the oil industry or if they have a lot of money," Buffett said.
Evaluating Treasury Secretary Steven Mnuchin, White House National Economic Council Director Gary Cohn, and Commerce Secretary-designate Wilbur Ross, Buffett said: "They're Wall Street guys. They're smart guys."
Ross, a billionaire who made his fortune investing in distressed assets, is expected to be confirmed in a Senate vote scheduled for Monday evening.
Mnuchin and Cohn were both Goldman Sachs alums.