MILWAUKEE — Last week, Sen. J.D. Vance (R-Ohio) was in the Senate, voting against Biden nominees, one to become a judge on the U.S. Court of Federal Claims and another to become a member of the Federal Labor Relations Authority.

On Wednesday night, he will deliver a prime time speech as Donald Trump’s vice-presidential pick, the most consequential moment of the 39-year-old freshman senator’s political career. It will cap a whirlwind 48 hours since Vance became Trump’s pick that he has spent in part writing his acceptance speech, which will focus heavily on his personal biography and how it ties to Trump’s “America First” movement, according to a person familiar with Vance’s plans.

Vance has otherwise kept a relatively low profile, but signs of the rapid transition from senator to running mate are evident: In a Tuesday morning walk with his family to Walgreens, he was flanked by his new security detail. He took a prominent seat next to Trump in the former president’s convention box Monday and Tuesday night. And he’s done a walk-through of the convention floor, where he saw his friend Donald Trump Jr. as they both prepare for their respective Wednesday night speeches.

The ensuing changes to Vance’s day-to-day are familiar to those who have experienced the transition from member of Congress to vice-presidential candidate. Al Gore got a call from then-Democratic candidate Bill Clinton just a few days before the 1992 Democratic National Convention while at his farm in Tennessee, according to Roy Neel, Al Gore’s chief of staff in his Senate and vice-presidential offices. By 5 a.m. the next day, Gore was on his way to Little Rock and “everything changed.”

“It was a whole different world. It was going to the Senate, which was a fairly predictable and in many respects a slow moving operation to just almost chaos every day,” Neel said. “Suddenly your entire schedule, your work plan, your travel all becomes a part and a subordinate to a different larger operation. In the Senate, you’re pretty much an island unto yourself.”

Vance’s nomination to the vice presidency also comes during an unprecedented presidential election: Trump on Saturday faced an attempted assassination at a Pennsylvania rally; the Democratic party is still debating whether President Biden should even be the party’s nominee amid questions about his mental acuity; and a former president and incumbent president are running against one another.

For all of Trump’s unpredictability, Vance was seen by many in Republican circles as his likely pick. Yet Trump kept the suspense going almost as long as possible, waiting until roughly an hour-and-a-half before Vance was officially nominated to the ticket.

At 2:04 p.m. on Monday, the first day of the Republican National Convention, it was official: Vance became the latest senator to be chosen as a running mate. (Vice President Harris, Biden and Gore were all previously U.S. senators before being selected as running mates.)

The Trump campaign had already hired an operations director for the running mate before the official announcement and Trump’s communications team is working with Vance’s team amid the transition, according to the person familiar with the dynamics. Vance’s campaign plane has a decal ready, but it’s not in Milwaukee.

Shortly after the announcement, Vance appeared on the convention floor with his wife Usha by his side. He shook hands with delegates as he approached the stage, and stood next to his friend U.S. Senate candidate Bernie Moreno, as Ohio Lieutenant Gov. Jon Husted made his nomination official.

Tuesday afternoon, the media and public got another brief glimpse of Vance when he visited the convention hall to practice his entrance onstage ahead of his Wednesday speech. Surrounded by a phalanx of staff and Secret Service agents, Vance looked around at the growing mass of media below him on the floor and ignored shouted questions about how he was feeling and his preparedness for the job.

Jake Kastan, who was a personal aide to former vice-presidential candidate Paul D. Ryan, said among the most biggest adjustments to being named a running mate is having a security detail and the schedule.

“Paul D. Ryan described it as being shot out of a cannon,” Kastan recalled. “You’re going from a routine day-to-day in the Capitol as a congressman to on many days visiting three different cities for four to five different events, fundraisers, rallies. Your schedule is so packed to 15 minute increments, so just that pace is quite exhilarating and a pretty big change from Congress ”

During the walk-through Tuesday, Vance spoke with a convention staffer out of earshot of the press, smiling for the cameras. His smile grew when his friend and running mate’s son Donald Trump Jr., walked up to him. The two hugged, and Vance jokingly asked whether anyone other than the journalists gathered below the stage to see him would show up for his speech.

Hours later, he was back on the convention floor, shaking hands and smiling. He greeted Arkansas Gov. Sarah Huckabee Sanders in Trump’s box. He also spoke to former New York Rep. Lee Zeldin (R-N.Y.) and Sen. Rick Scott (R-Fla.), as they waited for Trump to arrive.

A former Trump critic and now staunch ally, Vance rose to prominence in 2016 after writing the best-selling memoir Hillbilly Elegy about growing up in a steel mill community in Ohio in a family beset by drug addiction and poverty.

He served in the Marines, he went to Yale Law School, worked in business and is now a U.S. senator. Many Republicans viewed Trump’s decision to pick Vance as a sign he would be the former president’s successor, given that Trump can only serve one term. Yet Vance is one of the least experienced major party running mates in decades and has undergone a significantly rapid rise from becoming a freshman senator two years ago, said Joel Goldstein, an expert on the vice presidency and professor at St. Louis University School of Law.

“Being selected for a national ticket transforms someone’s life,” he said. “The fact that he’s historically inexperienced is noteworthy.”