Story highlights Ryan says he is now convinced Trump will advance the Republican agenda

A source close to Ryan said the speaker didn't give Trump a heads up

Washington (CNN) House Speaker Paul Ryan on Thursday said he's voting for presumptive GOP nominee Donald Trump.

In an op-ed for the Janesville Gazette of Janesville, Wisconsin, Ryan -- who sparked a political firestorm last month when he told CNN's Jake Tapper he was "just not ready" to back his party's nominee -- says he is now convinced Trump will advance the Republican agenda.

"I feel confident he would help us turn the ideas in this agenda into laws to help improve people's lives. That's why I'll be voting for him this fall," Ryan wrote.

He added, "It's no secret that he and I have our differences. I won't pretend otherwise. And when I feel the need to, I'll continue to speak my mind. But the reality is, on the issues that make up our agenda, we have more common ground than disagreement."

Late Thursday afternoon, Trump tweeted his appreciation for Ryan's support.

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