Republican presidential candidate Donald Trump formally endorsed House Speaker Paul Ryan for reelection on Friday night, after refusing to do so just days ago.

"We will have disagreements but we will disagree as friends and never stop working together toward victory," Trump said, delivering prepared remarks during a campaign rally in Green Bay, Wis.

"So in our shared mission to make America great again, I support and endorse our speaker of the House, Paul Ryan. He's a good man," Trump added, flashing a grin and two thumps up to a crowd in applause.

Trump also endorsed Arizona Sen. John McCain and New Hampshire Sen. Kelly Ayotte, two Republican leaders with whom he's feuded.

Trump, whose candidacy has been marked by frequent attacks on Republican leadership, changed his tune from just days earlier.

On Tuesday, Trump withheld his support for the House speaker's Wisconsin primary reelection, saying in an interview with The Washington Post, "I'm just not quite there yet," words that echoed Ryan's comments about his own initial hesitation to endorse Trump as presidential nominee back in May: "I'm just not ready to do that at this point. I'm not there right now."

Paul Ryan and other elected Republicans haven't held back criticism for Trump either.

Signs of GOP divisions manifested most recently in Republican reactions to Trump's response to Khizr Khan, a Muslim father who spoke at the Democratic convention about his soldier son who was killed in Iraq in 2004, as NPR Politics' Amita Kelly previously reported:

Ryan said he "rejects" any religious test for entering the country — a clear jab at one of Trump's evolving immigration proposals — and that "Captain Khan was one such brave example" of Muslim-Americans who have "served valiantly in our military and made the ultimate sacrifice."

On Monday, Sen. John McCain, whom Trump once mocked for being captured during the Vietnam War, rebuked Trump's comments about the Khans.

"I hope Americans understand that the remarks do not represent the views of our Republican Party, its officers, or candidates," McCain said in a nearly 700-word statement.

The dividing lines appear to extend as far as the GOP ticket: Vice presidential nominee Mike Pence told Fox News on Wednesday that he endorses Ryan, contradicting Trump's refusal to endorse Ryan on Tuesday.

As for Trump's critiques of the Khans, Pence gestured reconciliation in a statement, saying, "Donald Trump and I believe that Captain Humayun Khan is an American hero and his family, like all Gold Star families, should be cherished by every American."

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