Paul Ryan
Paul RyanReuters

House Speaker Paul Ryan on Thursday finally declared his support for presumptive Republican presidential nominee Donald Trump.

In an op-ed for the Janesville Gazette of Janesville, Wisconsin, Ryan wrote that 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 in the op-ed, quoted by CNN.

"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," added Ryan.

The Speaker’s backing for Trump comes after he said last month he is “not yet ready” to support Trump, to which the billionaire responded by saying he was not ready to support Ryan’s agenda.

The two held a meeting several weeks ago, following which they released a statement in which they stressed the importance of “unity” in the Republican party.

A source close to Ryan told CNN he had made the decision earlier in the week, but declined to speak on the discussions between the two, saying the op-ed "speaks for itself."

"He didn't give Mr. Trump a heads up. This was always going to be the speaker's own decision on his own timeline," the source said.

Democrats on Thursday appeared eager to use the endorsement against the entire Republican brand, once again arguing there is no distance between any Republican congressional candidate and Trump.

"House Republicans will be inseparably tied to their toxic front-runner in November, case closed," said Meredith Kelly, a spokesman for the Democratic Congressional Campaign Committee.

News of Ryan’s support for Trump broke just as the likely Democratic nominee, Hillary Clinton, began a foreign policy speech in San Diego in which she attacked Trump as a threat to national security.

Ryan criticized Clinton in his op-ed, writing, "A Clinton White House would mean four more years of liberal cronyism and a government more out for itself than the people it serves. Quite simply, she represents all that our agenda aims to fix."