“To be perfectly candid… I’m just not ready to do that at this point,” Ryan told CNN.

“I hope to though, and I want to. But I think what is required is that we unify this party.”

It was a stunning declaration expected to reverberate throughout the party’s establishment and its rank and file, amid swirling concerns over whether conservatives will rally around Trump in his expected election matchup against Democrat Hillary Clinton.

Ryan, who repeated he would not accept the nomination in case of a contested convention, was the Republican vice presidential nominee in 2012 and is currently second in line to the presidency.

While his role as House Speaker makes him a quintessential symbol of the Washington establishment that Trump supporters loathe, his public doubts about the standardbearer could filter down to millions of voters.

“He’s got some work to do,” Ryan said, noting that “the bulk and the burden” was on Trump to begin the healing after a brutal primary campaign and the brash billionaire’s string of insulting remarks about other candidates, Muslims, Mexicans, refugees, women and others.

“It’s time to set aside bullying. It’s time to set aside belittlement,” Ryan said.

Thursday’s comments were all the more startling because Trump has now emerged as the party’s standardbearer and Ryan will be co-chairman of the Republican presidential nominating convention in July.

– Work together? –

Trump shot back within minutes.

“I am not ready to support Speaker Ryan’s agenda,” he said in a statement.

“Perhaps in the future we can work together and come to an agreement about what is best for the American people.”

Trump won Tuesday’s hotly contested Indiana primary, pushing Ted Cruz and John Kasich out of the race and leaving him as the presumptive nominee.

Democrats seized on the Trump-Ryan clash to highlight the divisions and turmoil within the GOP.

“Well, that was awkward,” Democratic National Committee spokesman Mark Paustenbach said in a statement.

“Bring a hazmat suit if you’re one of the remaining Republican leaders still planning to stand with your nominee,” Paustenbach added. “Trump has gone radioactive.”

Ryan insisted that despite his misgivings about Trump, no Republicans should support Clinton — as several have threatened to do.

“We need a standardbearer that can unify all — all conservatives and the wings of the party — and then go to the country with an appealing agenda,” he said.

Ryan is the latest in a string of party grandees who have declined to back Trump.

Presidents George H.W. Bush and his son George W. Bush have signalled they will not endorse, while Mitt Romney, the 2012 nominee, is reportedly declining to attend the Republican convention.

Some conservatives, including freshman Senator Ben Sasse of Nebraska, argue that a third candidate should challenge Trump and Clinton.

“Why are we confined to these two terrible options?” Sasse asked in an open letter to US Republicans. “If both choices stink, we reject them and go bigger.”

Ryan put himself at odds with Senate Republican leader Mitch McConnell, who publicly endorsed Trump’s candidacy “to prevent what would be a third term of Barack Obama.”

“As the presumptive nominee, (Trump) now has the opportunity and the obligation to unite our party around our goals,” McConnell said in a statement Wednesday.

Trump, 69, has said Republicans would unite to support him.

“Now we’ll unify the party,” Trump told Fox News on Wednesday. “We’re going to get people together.”

But with sky-high unfavorability ratings, and concern within his own party about his temperament, the real estate mogul sought to assuage concerns about how a President Trump would govern.

“Things will be fine,” he told The New York Times. “I’m not running for president to make things unstable for the country.”

As Trump seized the GOP mantle, a CNN poll highlighted the formidable challenge facing him.

It found Clinton, hoping at 68 to become America’s first female commander-in-chief, leading the tycoon 54 percent to 41 percent.

Nevertheless, the former secretary of state suffered a shock loss in Indiana to Bernie Sanders, who has pledged to remain in the race until the end despite the delegate math overwhelmingly favoring Clinton.

Clinton has already pivoted to Trump and their general election matchup.

“He is a loose cannon, and loose cannons tend to misfire,” she said.

Trump, appearing in West Virginia coal country late Thursday for his first rally since becoming the inevitable nominee, hammered Clinton on trade, the Clinton Foundation, and her vow to kill coal jobs — comments for which she has apologized.

Standing in front of miners holding signs reading “Trump Digs Coal,” he pledged to re-open mines and put people back to work.

“Miners, get ready because you’re going to be working your asses off,” he said.

He made no mention of Ryan at the rally.

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