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Former New Jersey Gov. Chris Christie had some simple advice for President Donald Trump about the ongoing Russia investigation: Keep quiet.

Trump, however, has ignored him, Christie said Tuesday.

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Christie spoke with MSNBC's "Morning Joe" as he promotes his new book, "Let Me Finish: Trump, the Kushners, Bannon, New Jersey, and the Power of In-Your-Face Politics." He was asked by co-hosts Mika Brzezinski and Joe Scarborough about his advice to Trump on how to handle special counsel Robert Mueller's ongoing investigation into Russian interference in the 2016 presidential election and whether the Trump campaign colluded with Russian officials.

Christie said he told Trump not to "be fooled" by what his "C-level legal team" was telling him about the investigation wrapping up promptly. Christie, a former federal prosecutor, said he's known Mueller for years and insisted the probe would take "a long time."

"There's no way you can make this investigation shorter, but there's lots of ways you can make it longer," Christie recalled telling Trump. "And the way you can do that is to keep talking about it and tweeting about it, because every time you do that, prosecutors say, 'Great, more things for us to chase down.'"

"I can tell you that I must have said this to him two dozen times over the last two years: 'You need to stop, you're making this worse,'" he added.

Christie said Trump was ignoring his advice even though he knows it's "good."

Christie, a Republican and a Trump ally, was asked why Trump keeps taking advice from his son-in-law and adviser, Jared Kushner, with whom Christie has had a fraught history dating to Christie's days as a federal prosecutor in New Jersey, when he sent Kushner's father to prison on tax evasion and other charges.

"I don't know. Makes no sense to me," Christie said.