Speaker of the House Paul Ryan said Thursday that he’s “not ready” to support Donald Trump for president despite his status as the presumptive Republican nominee.

"I'm just not ready to do that at this point. I'm not there right now,” Ryan said in an interview with CNN.

Ryan is the highest ranking Republican to publicly express doubt about the New York businessman’s ability to unit the party and, ultimately, win the White House.

The comments are a departure for Ryan, who has insisted for months that he will support the GOP nominee. He has used his position as speaker and chairman of the Republican National Convention to maintain neutrality throughout the raucous primary season, often declining to answer questions about Trump or the presidential contest in general.

Now, just two days after Trump won a decisive victory in Indiana that forced his remaining rivals, Texas Sen. Ted Cruz and Ohio Gov. John Kasich, to drop out of the race, Ryan said there is work to be done before he will line up behind Trump.

Ryan, who was his party’s 2012 vice presidential nominee, said he only started considering whether he could support Trump as the standard-bearer after that Indiana victory, and that he had been expecting the race to go through the California primary on June 7 or to a contested convention in Cleveland this summer.

"I thought about this two days ago,” Ryan said. “I thought, actually, this thing was going to go to June 7 at the very least -- probably to a convention -- and so this is all pretty new for us.”

Ryan told CNN he hoped Trump would unify “all wings of the Republican Party and the conservative movement" and that his campaign would give voters "something that they're proud to support and proud to be a part of."

"And we've got a ways to go from here to there," he added.

In a statement issued Thursday afternoon, Trump turned the tables on Ryan, saying he is "not ready to support Speaker Ryan's agenda. Perhaps in the future we can work together and come to an agreement about what is best for the American people. They have been treated so badly for so long that it is about time for politicians to put them first!"

A major role for Ryan this fall will be to keep his majority in the House and to help Republicans hold the Senate. He’s delivered a policy blueprint for his caucus and raised $17 million in the first quarter of 2016.

A source familiar with Ryan’s thinking told RealClearPolitics that unifying the party and pursuing a conservative agenda, along with preserving the House majority, were key to Ryan’s decision not to endorse Trump just yet.

“This is something that obviously Speaker Ryan has given a lot of thought to and his two top priorities are advancing this conservative policy agenda that House Republicans are working on right now and maintaining the majority of the House,” the source said. "Those are two things he’s working really hard on, they’re at the front of his mind, so it’s safe to say those two things obviously are part of this whole discussion.”

His decision not to back Trump represents a break from his Senate counterpart, Majority Leader Mitch McConnell, along with Republican National Committee Chairman Reince Priebus, who have both said it is time for the party to rally around their nominee.

“I have committed to supporting the nominee chosen by Republican voters, and Donald Trump, the presumptive nominee, is now on the verge of clinching that nomination,” McConnell said Wednesday evening. “Republicans are committed to preventing what would be a third term of Barack Obama and restoring economic and national security after eight years of a Democrat in the White House. As the presumptive nominee, he now has the opportunity and the obligation to unite our party around our goals.”

Meredith Kelly, a spokeswoman for the Democratic Congressional Campaign Committee, called Ryan’s comments “cowardice veiled as bravery” and “too little, too late.”

“‘Not there right now’ is just another one of the toothless statements that have become Ryan’s hallmark since becoming Speaker,” Kelly said in a statement. “For months, Paul Ryan refused to take on or rebuke Trump by name as he demeaned women, refused to disavow the KKK, or insulted Hispanics. Trump is now poised to accept the GOP’s nomination, and Ryan is scrambling because he knows what everyone else knows: Donald Trump is toxic for his own reputation, and for House Republicans.”