"His ... plan to put on a 35 percent tariff for goods imported into the United States from Mexico and China would sink this country into a recession," she told CNBC's "Squawk on the Street." "It would penalize global companies who are trying to be competitive globally."
Those tariffs would also hurt U.S.-based workers of American multinational companies and make foreign products more expensive for consumers and businesses, she said.
"I think he doesn't fully grasp the law of unintended consequences of what seems like a silver bullet, a quick fix. There are no silver bullets and quick fixes to our problems in the United States," said Whitman, a Republican who ran unsuccessfully for California governor in 2010.
The country needs a thoughtful, experienced leader with the temperament to unite the American people, and Trump is not that person, she said.