US House Speaker Paul Ryan says he will vote for the Republican presidential candidate Donald Trump in this year’s election, despite their differences.
Mr Ryan wrote in a newspaper column “we have more common ground than disagreement”.
Mr Trump’s rise has alarmed senior Republicans. Last month Mr Ryan said he was “not ready” to back him.
But the endorsement is the latest sign the party is unifying around the party’s presumptive nominee.
“I’ll be voting for @realDonaldTrump this fall,” Mr Ryan tweeted. “I’m confident he will help turn the House GOP’s [Republican Party] agenda into laws.”
Explaining his decision further, he wrote in his hometown Gazette newspaper in Wisconsin: “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.”
He also attacked Mr Trump’s likely Democratic opponent, Hillary Clinton.
“A Clinton White House would mean four more years of liberal cronyism and a government more out for itself than the people it serves,” he said.
As House Speaker, Paul Ryan is the most senior elected Republican official in the country. He and Mr Trump have held a series of talks to try to find common ground.
“We’re not playing word games, feel free to call it an endorsement,” one of Mr Ryan’s advisors, Brendan Buck tweeted.