The "greatest risk" to President Donald Trump's presidency and businesses is not Special Counsel Robert Mueller, but federal prosecutors in New York, according to Alan Dershowitz.

Dershowitz, a Harvard Law professor emeritus, explained on "Fox & Friend" on Monday that Trump has constitutional defenses to Mueller's Russia probe, but that is not the case with respect to the investigations being conducted by the U.S. Attorney's Office for the Southern District of New York.

He noted that last week federal prosecutors secured a guilty plea from longtime Trump attorney Michael Cohen and granted immunity to the Trump Organization’s chief financial officer, Allen Weisselberg.

A source told Fox News that Weisselberg’s immunity agreement was related to the grand jury probe into Cohen’s personal business dealings, including his hush money payments to two women, Stormy Daniels and Karen McDougal, who allege they had affairs with Trump.

"These are business investigations," Dershowitz explained. "And of course, the president can't be indicted, but his businesses can be indicted."

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He said investigators can look into the inner workings of Trump's businesses, including loans secured, foreign investment and foreign involvements.

"If I were Trump's lawyers, I'd be focusing all of my defense efforts on the Southern District, and let the Mueller probe go. I don't think it's going anywhere, but the Southern District raises some real red flags for Trump's businesses," Dershowitz said.

He noted that his friend Harvey Silverglate wrote a book titled "Three Felonies A Day," which says that if a U.S. attorney's office investigates any complicated business, they are going to uncover several federal crimes every day.

"That's the way the laws are written. If you look hard enough, you're going to find something. And they're looking very, very hard," Dershowitz said.

"It's targeting people. And if they can target President Trump, they can target you. They can target anyone. That's the problem."

Watch more from Dershowitz above.

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