TAMPA, Fla. >> Hillary Clinton’s search for a vice president started with a commanding victory in the New York primary and a special delivery in a plastic Duane Reed bag. Three months later, it ended with a phone call to a shipyard office, where Virginia Sen. Tim Kaine was waiting.

From the start, Kaine was a front-runner to join Clinton on the Democratic ticket. A senator, former Virginia governor and mayor of Richmond, he hails from a top battleground state and, as a fluent Spanish speaker, could help in another: Florida. Victories in both would likely put the White House out of the reach of Donald Trump and his running mate, Indiana Gov. Mike Pence.

But Clinton grew personally comfortable with the likable and even-keeled Kaine as they campaigned together in recent weeks and discussed the vice presidency. Clinton ultimately concluded that she had “unshakeable confidence in Kaine’s readiness to do the job,” according to a Clinton aide familiar with her thinking. The aide spoke on condition of anonymity to describe the private deliberations over her selection.

For a presidential candidate with the unique experience of helping conduct her husband’s 1992 search for a vice president — it ended with the choice of Al Gore — along with eight years at the White House and another four years as President Barack Obama’s secretary of state, that kind of confidence mattered.

It wasn’t an easy decision. Clinton was also drawn to Agriculture Secretary Tom Vilsack, the former Iowa governor who remained in the running until the end. A person close to the campaign, also speaking on condition of anonymity to discuss the private deliberations, said Clinton had a hard time not choosing her longtime family friend and political loyalist.

Campaign chair John Podesta started the process after Clinton’s convincing victory over Democratic rival Bernie Sanders in April’s New York primary, dropping off binders of information with Clinton at her home in Chappaqua, New York. The information on potential running mates was delivered in a bag from Duane Reed, a New York drug store.

As Clinton dealt with an up-and-down series of primary contests against Sanders, her team delved deeply into several potential running mates, scouring public information and ultimately asking a select few to provide detailed financial and personal information, and consent to interviews.

Clinton’s team maintained a tight control over the information. Her screeners included Washington attorney James Hamilton, former State Department chief of staff Cheryl Mills and Podesta, along with a group of attorneys and top aides.

As the process entered July, Clinton scheduled a joint campaign event with Kaine in Annandale, Virginia, where he showed off his bilingual abilities, telling the audience, “Estamos listos para Hillary!” — or “We’re ready for Hillary.”

Clinton and Kaine met that evening at her Washington home for 90 minutes, and she invited Kaine and his wife, Virginia Education Secretary Anne Holton, to her home in Chappaqua two days later. This time, lunch was served and the Kaines joined Bill Clinton and the Clintons’ daughter, Chelsea, and son-in-law, Marc Mezvinsky.

Kaine’s name remained at the top of the speculation for vice president, but he kept his head down, telling reporters that he enjoyed being senator. Just hours before his selection, he professed that he didn’t know where things stood.

While Clinton also considered other potential running mates, including Labor Secretary Tom Perez, New Jersey Sen. Cory Booker and Massachusetts Sen. Elizabeth Warren, officials said the choice came down to Kaine and Vilsack.

Clinton campaigned for Vilsack in his 1998 comeback victory as Iowa governor, and he later stood by her through her difficult 2008 presidential campaign. They served together in Obama’s Cabinet.

The person familiar with the search process likened Vilsack to the “heart” candidate, given his friendship with Clinton, but said that Kaine’s experience as a winner in a pivotal swing state along with his Senate experience in foreign affairs helped put him over the top.

While Kaine had supported Obama, not Clinton, in the 2008 presidential primaries, the presumptive Democratic nominee noted in a recent interview that Kaine had never lost an election during a lengthy political career that began with a seat on the Richmond city council during Bill Clinton’s first term in the White House.

The Clinton aide said she ultimately concluded that Kaine met her top consideration — the ability to step in as president if necessary — and she had reached a comfort level with the low-key lawmaker that made her believe he could be a “true partner in governing.”

Podesta, who served as chief of staff to Bill Clinton and later advised Obama, offered the former secretary of state this advice: “It needs to be someone who whenever they walk into the room, you are glad to see them and you want to have them as part of any conversation.”

The offer finally came in a 7:32 p.m. EDT phone call from Clinton, who was in a holding room after wrapping up a rally at the Florida state fairgrounds in Tampa. Kaine was attending a fundraiser in Newport, Rhode Island, for the state’s Democratic senator, Jack Reed. Taking the call in a shipyard office, he quickly accepted.

Clinton then called Obama at the White House about 20 minutes later to inform him of her decision. Shortly after 8 p.m., the campaign blasted out a text message and accompanying announcement on Twitter that she had made her choice.

“I’m thrilled to announce my running mate, timkaine, a man who’s devoted his life to fighting for others,” Clinton said on Twitter.

Replied Kaine: “Just got off the phone with Hillary. I’m honored to be her running mate. Can’t wait to hit the trail tomorrow in Miami!”