Former President Donald Trump chose Sen. JD Vance of Ohio as his running mate on Monday, picking a onetime critic who became a loyal ally and is now the first millennial to join a major-party ticket at a time of deep concern about the advanced age of America’s political leaders.

“After lengthy deliberation and thought, and considering the tremendous talents of many others, I have decided that the person best suited to assume the position of Vice President of the United States is Senator J.D. Vance of the Great State of Ohio,” Trump said in a post on his Truth Social network as the Republican National Convention got underway in Milwaukee.

The 39-year-old Vance rose to national fame with the 2016 publication of his memoir, “Hillbilly Elegy.” He was elected to the Senate in 2022 and has become one of the staunchest champions of the former president’s “Make America Great Again” agenda, particularly on trade, foreign policy and immigration.

But he is largely untested in national politics and is joining the Trump ticket at an extraordinary moment. An attempted assassination of Trump at a rally Saturday has shaken the campaign, bringing new attention to the nation’s coarse political rhetoric and reinforcing the importance of those who are one heartbeat away from the presidency.

Vance himself faced criticism in the wake of the shooting for a post on X that suggested President Joe Biden was to blame for the violence.

“The central premise of the Biden campaign is that President Donald Trump is an authoritarian fascist who must be stopped at all costs,” Vance wrote. “That rhetoric led directly to President Trump’s attempted assassination.”

Law enforcement has not yet specified a motivation for the shooting.

Why Vance was chosen over the other finalists

Vance, Trump said, “will be strongly focused on the people he fought so brilliantly for, the American Workers and Farmers in Pennsylvania, Michigan, Wisconsin, Ohio, Minnesota, and far beyond.” Several of those Midwestern states are expected to play a critical role in November’s election.

Trump and Vance spoke about 20 minutes before the Truth Social post and Trump formally offered him the job, according to a person familiar with the call who, like others, requested anonymity to share the private conversation.

Biden’s reelection campaign issued a statement calling out Vance for saying, had he been vice president, he would have allowed “multiple slates of electors” to challenge Biden’s victory over Trump four years ago. Trump repeatedly promoted falsehoods about election fraud before and after Jan. 6, 2021, when rioters loyal to the former president stormed the Capitol to try to stop the certification of his loss.

“Donald Trump picked J.D. Vance as his running mate because Vance will do what Mike Pence wouldn’t on January 6: bend over backwards to enable Trump and his extreme MAGA agenda, even if it means breaking the law and no matter the harm to the American people,” Biden campaign chair Jen O’Malley Dillon said in the statement.

Florida Sen. Marco Rubio and North Dakota Gov. Doug Burgum, the other contenders on Trump’s shortlist, had been informed earlier Monday afternoon that they were not his pick, according to people familiar with their conversations.

Conversations in the last 10 days between Rubio and Trump’s campaign had focused on concerns about the residency issue and how they would work around both men residing in the same state, according to a person familiar with the private talks who insisted on anonymity to discuss them.

The Trump campaign wanted to be 100% sure that there would not be a protracted legal battle over the issue, and Rubio was unwilling to uproot his family, the person said.

Trump had spent months testing the field, assessing how his contenders performed on television, at fundraisers and on rally stages. Several, including Burgum and Vance, joined him at his criminal hush money trial in New York. Others were there at the debate last month, where Biden’s disastrous performance upended his campaign, leading to widespread calls for him to step aside in favor or a younger candidate.

The pick is sure to energize Trump’s loyal base. Vance has become a fixture on the conservative media circuit and frequently spars with reporters on Capitol Hill, helping establish him as the kind of leader who could carry Trump’s mantle into the future, beginning with the next presidential election in 2028.

But the pick also means that two white men will now lead the Republican ticket at a time when Trump has sought to make inroads with Black and Latino voters.

In “Hillbilly Elegy,” Vance detailed life in Appalachian communities that drifted from a Democratic Party many residents found disconnected from their daily travails. While the book was a bestseller, it was also criticized for sometimes oversimplifying rural life and ignoring the role of racism in modern politics.