Donald Trump announced today that he had selected J.D. Vance as his running mate, elevating the 39-year-old Senator and former Marine who transformed over the last few years from a sharp critic of the former president into one of his most loyal allies.

The selection was made public on the first day of the Republican National Convention, where Trump was officially awarded enough delegates to become the party’s nominee for president. By choosing Vance, Trump tapped an ambitious ideologue who relishes the spotlight and has already shown he can energize donors. Here’s what to know about him.

Vance in 2016 privately feared that Trump could be “America’s Hitler,” and publicly called him “reprehensible.” But by the time he ran for Senate in 2021, he had adopted much of Trump’s ring-wing messaging, such as advancing Trump’s unsubstantiated claims about widespread election fraud and hard-line stances on immigration.

Vance’s selection positions him to continue pushing Trump’s movement after a potential second term. His similarities with Trump suggest a limited potential to draw in new voters — but Trump has never seen much of a need for a vice president, and part of the delay in his selection was Trump’s lack of interest in the position, my colleague Maggie Haberman reported.

Trump’s announcement came just days after he survived an assassination attempt, an episode that underlined the significance of his choice. And even as Trump called for unity, Vance directly attributed the shooting to the rhetoric of President Biden and his campaign.

In other politics news, the latest New York Times/Siena College polls found that President Biden is trailing Trump in Pennsylvania and is just slightly ahead in Virginia, two must-win states. Vice President Kamala Harris ran about two percentage points ahead of Biden.