Washington (CNN) A former New Jersey governor is urging fellow Republicans to call on President Donald Trump to resign following his embrace of Russian President Vladimir Putin at the Helsinki summit last week.

In an op-ed published in the Los Angeles Times earlier this week, Christine Todd Whitman wrote that Trump's recent behavior toward Russia and his performance at the Helsinki summit reveal that he is "unfit for office."

"We must put aside the GOP label, as hard as that may be, and demonstrate the leadership our country needs by calling on the president to step down," Whitman wrote.

Whitman also defended special counsel Robert Mueller's investigation into Russian election interference and called on Republicans to stand for "country over party."

"In this election year, opposing Trump is risky for GOP candidates," Whitman said. "Invoking the need to choose country over party is an overused trope. But it is essential now."

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