Sam Zell: Why I didn't go into business with Donald Trump

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Real estate tycoon Sam Zell said Tuesday he turned down Donald Trump's offer to enter into a partnership because the two simply have contrary approaches to doing business.

"I did my best for many, many years to stay as best under a rock as I possibly could. That was the way I approached doing business. Donald's approach is obviously very different," the chairman of Equity Group Investments told CNBC's "Squawk Box."

"You don't see my name on any buildings, do you? That's just not who I am. Far be it for me to criticize anybody else for whatever they want to do," he said.

As for Trump's presidential candidacy, Zell said there's a huge difference between someone being your day-to-day business partner and your political leader.

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In October, Zell told "Squawk Box" he didn't think Trump had the temperament and personality to be the president, though he cautioned that the now-presumptive GOP presidential nominee shouldn't be underestimated.

On Tuesday, Zell reiterated his call that Trump shouldn't be underestimated, but said "the definition of temperament required has changed in the last 12 weeks." Both Democrats and Republicans have hardened, and the nation is in for an enormous battle, Zell said.

Zell said he has never publicly endorsed a candidate, and he is not about to start. However, he said the greatest risk of the 2016 election is that one party's philosophies become too embedded in the executive office.

"If we have the same party in control of the executive branch in the next four years, we will have had 12 years of executive control, and that begins to change the basic patterns and framework of how our country works," he said.