In a bid to bridge party divisions, Donald Trump formally endorsed prominent elected Republican leaders during a campaign rally on Friday, in Green Bay, Wis. Evan Vucci/AP hide caption

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President Obama slammed Republican nominee Donald Trump as "unfit" and "woefully unprepared" to be president during a news conference with Singapore's prime minister at the White House on Tuesday. Pablo Martinez Monsivais/AP hide caption

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NPR's Steve Inskeep interviews Speaker of the House Paul Ryan in the Speaker's conference room at the U.S. Capitol in Washington, D.C. Ariel Zambelich/NPR hide caption

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House Speaker Paul Ryan of Wisconsin meets with reporters on Capitol Hill in Washington on Thursday after his meeting with Republican presidential candidate Donald Trump. Cliff Owen/AP hide caption

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Republican presidential candidate Donald Trump arrives for a meeting with House Speaker Paul Ryan at the Republican National Committee Headquarters on Capitol Hill Thursday. Andrew Harnik/AP hide caption

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