The Republican Party is splitting in two
Less than a day later, John Kasich called it quits, as well.
Trump was the presumptive, newly unchallenged Republican presidential nominee.
Something completely unprecedented happened Thursday afternoon: The top elected Republican official decided to refrain from supporting the party's new standard-bearer off the bat.
"I'm just not ready to do that at this point," Ryan told CNN host Jake Tapper in an interview. "I'm not there right now."
"I hope to, and I want to," he continued. "But I think what is required is to unify this party. And I think the bulk of the burden on unifying the party will have to come from our presumptive nominee."
Rather than unification, the Republican Party is in the midst of a virtual split in two with Trump as the party's presumptive nominee. Many elected officials and party leaders have come out in support of the mogul, including Republican National Committee Chair Reince Priebus and Senate Majority Leader Mitch McConnell, in hopes of rallying the party around a strong challenge to likely Democratic nominee Hillary Clinton.
Others have held their ground. The party's last two presidential nominees and its remaining two living presidents declined to offer their support. Ryan was the loudest chip to fall (at least for now) in the camp.
"I think what a lot of Republicans want to see is that we have a standard bearer that bears our standards," he said Thursday.
Trump did little to hold back in retaliation toward Ryan, signaling a clear and perhaps lengthy rift within the party. On Thursday, he released a statement saying he was "not ready" to back the speaker's policy agenda.
The next day, he attributed Ryan's weariness to the real-estate magnate's repeated bashing of 2012 GOP presidential nominee Mitt Romney's performance in the 2012 election. Ryan was Romney's running mate.
"Well they lost a race that should've been won last time, and I've been very open about it," Trump told "Fox & Friends" in a Friday interview. "That was a race that should've easily been won. That was an easier race than we have this year but I'll win. You already see the polls going up rapidly."
"I mean he talks about unity, but what is this about unity?" Trump continued.
On Sunday, Trump claimed he had been "blindsided" by Ryan's non-endorsement. In a "Meet the Press" interview, Trump wouldn't rule out trying to replace Ryan as the chair of this summer's Republican National Convention.
Yet Ryan is hardly alone in his refusal to support Trump.
Some of the most influential members of the Republican Party are planning to sit out Trump's coronation at the Republican National Convention this summer.
The past two Republican presidents and four of the past five GOP presidential nominees have announced that they'll be skipping the convention.
Romney, the 2012 nominee who campaigned hard against Trump in recent months while propping up his competitors, said he wouldn't be attending the convention. John McCain, an Arizona senator who was the nominee in 2008, won't be attending the convention but said he would vote for Trump.
Both Presidents George H.W. Bush and George W. Bush plan to stay out of the presidential election completely.
On Friday, 2016 GOP presidential contenders Lindsey Graham and Jeb Bush both said they couldn't support Trump, as well. Trump lashed out in furious responses that were reminiscent of his many battles with his two former rivals.
"I fully understand why Lindsey Graham cannot support me," Trump said. "If I got beaten as badly as I beat him, and all the other candidates he endorsed, I would not be able to give my support either."
Others, such as Ben Sasse, a Nebraska senator, have been floating the idea of a third-party candidate running on a conservative platform. When MSNBC's "Morning Joe" co-host Joe Scarborough offered the idea on his Friday show, an angered Trump took to Twitter to lash out at him, as well.
"Joe Scarborough initially endorsed Jeb Bush and Jeb crashed, then John Kasich and that didn't work," Trump tweeted. "Not much power or insight!"
"I hear @JoeNBC of rapidly fading @Morning_Joe is pushing hard for a third party candidate to run," he posted moments later. "This will guarantee a Crooked Hillary win."
Many Republicans who previously declined to line up behind the Manhattan billionaire have since reversed course. But his most likely general-election opponent has already taken full advantage of the infighting within the GOP.
Clinton's campaign has pushed out emails to reporters almost every time a prominent Republican has distanced himself or herself from Trump. The campaign also cut a video quoting Jeb Bush, Graham, Ted Cruz, and Marco Rubio - all his former rivals - saying negative things about the business mogul.
Priebus, the Republican National Committee chair, has been trying his best to mend the fences. Both Trump and Ryan will meet with the party's chairman after meeting with each other on Capitol Hill next week. Priebus, who called for party unity after anointing Trump the presumptive nominee following Indiana, is looking to make due on that pledge.
And it would appear necessary. The Cook Political Report adjusted a dozen states' ratings with Trump as the nominee of a fractured party, saying those states had all become more favorable to Democrats in the presidential election.
But as Trump made clear on Wednesday's edition of "Morning Joe," he doesn't really care for party unity.
"I don't think it's imperative that the entire party come together," he said. "I don't want everybody. I don't even want certain people that were extraordinarily nasty. Let them go their own way. Let them wait eight years or let them wait 16 years or whatever."