Trump's endorsements came at a rally in Green Bay, Wisconsin.

"We will have disagreements, but we will disagree as friends and never stop working together toward victory. And very importantly, toward real change," Trump said, reading off a prepared statement. "So in our shared mission, to make America great again, I support and endorse our speaker of the House, Paul Ryan."

Trump earlier in the week had declined to endorse Ryan and McCain, as well as New Hampshire Sen. Kelly Ayotte.

"And while I'm at it, I hold in the highest esteem Sen. John McCain for his service to our country in uniform and in public office, and I fully support and endorse his re-election," said Trump, before backing Ayotte.

The real estate mogul's campaign immediately sent out a list-building email to supporters, writing, "It's time to unite our Party and deny a third term of Obama. I have officially endorsed Paul Ryan -- and together, we will fight for YOU, and together we will Make America Great Again!"

Trump's endorsements came more than 10 minutes after he began reading his statement, cutting in several times to offer tangential remarks -- from again rehashing an incident involving a crying baby at a recent rally to touting the strength of his fundraising.

Trump heavily emphasized his outsider status in the lead-up to delivering his endorsements of three incumbent Republicans with a combined tenure in Congress of more than a half century.

"It's time to change a rigged political system that works only for the insiders and to replace it with a government that serves the people," Trump said.

But then, Trump pointed out that he owes his success to his ability to put together "a really fantastic team" and stressed that he would need a Republican House and Senate to accomplish his agenda as president.