Story highlights Christie told reporters he's been upfront with Trump about how he feels about him using the social media

He also defended Trump's feud with the London mayor

Washington (CNN) New Jersey Gov. Chris Christie said Tuesday that President Donald Trump's use of Twitter sometimes "hasn't been for his best interest."

Christie told reporters in Mendham Township, New Jersey, that he's been upfront with Trump about how he feels about the President using social media.

"I've said many times both publicly and to the President directly -- and I am not in a small group of people who have said this to him -- that I think Twitter is a great tool when used the right way," he said in response to a question by CNN's Shachar Peled. "And I think many times he's used it the right way to get his message out there and have people hear directly from him what he thinks, and other times I think what he's done hasn't been in his best interest."

He continued: "And all I care about is what's in the best interest of the President because that's what's in the best interest of the country. So I'm not going to get into critiquing every tweet."

Christie was speaking to reporters as New Jersey voters head to the polls to select the Republican and Democratic candidates to succeed him as governor.

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