Trump announced Ohio Sen. J.D. Vance will be his running mate, writing on Truth Social that the Ohio Republican is "the person best suited to assume the position of Vice President of the United States."

The decision caps off months of speculation and sees Trump elevate a 39-year-old first-term senator whose roughly year and a half tenure in the Senate has seen him emerge as a staunch ideological ally of the former president.

MORE | Trump VP pick: Former president announces Vance as his running mate

The Republicans have passed their party platform, despite dissent from the evangelical wing over softened language on abortion that better matches Trump's current posture. A fair amount of "nayes" were heard in the convention hall, but not enough for the vote to fail.

Rep. Michael Waltz, R-Fla., told delegates that the "platform was personally approved by President Donald J. Trump."

"It's a different kind of platform," said platform co-chair Sen. Marsha Blackburn, R-Tenn., as she presented the platform for a vote.

"It is not a laundry list of special interests' wishes, but a succinct, clear agenda and a promise to the American people."

Before the overwhelming voice vote in Milwaukee, the platform had passed 84-14 by the platform committee.

Donald Trump's son, Eric Trump, announced on X that he'll be casting the vote at 3:30 p.m. ET declaring his father the Republican nominee for president.

He lives in Florida and is expected to cast the vote with Florida's delegation, putting Trump over the top with enough delegates to formally become the nominee.

North Dakota Gov. Doug Burgum has been told he is not Trump's running mate pick, three sources familiar with the matter tell ABC News.

Trump's pick is expected to be announced at some point Monday.