In an extraordinary rebuke of the Republican Party’s presumptive presidential nominee, House Speaker Paul D. Ryan (Wis.), the nation’s highest-ranking GOP official, said Thursday that he could not support Donald Trump until he changes his tone and demonstrates that he shares the party’s values.

While acknowledging that Trump has mobilized a powerful grass-roots movement and earned the nomination, Ryan said that Trump has not shown himself to be “a standard-bearer who bears our standard” — and he put the onus on the business mogul to re-calibrate his campaign and offer a more inclusive vision.

Asked by CNN anchor Jake Tapper whether he backs Trump, Ryan responded: “I’m just not ready to do that at this point. I’m not there right now. And I hope to, though, and I want to. But I think what is required is that we unify the party. And I think the bulk of the burden on unifying the party will have to come from our presumptive nominee.”