Joe Biden announced Tuesdaythat he has chosenSen. Kamala Harris (D-Calif.) as his running mate— the first Black woman to be named to a major-party U.S. presidential ticket, and potentially the first woman vice president if Biden defeats President Trump.

The big picture: Harris was probably the safest choice Biden could have made among his running mate finalists. She has a national profile and experience with elected office, was vetted and tested in the Democratic presidential primaries and can boost Biden's fundraising.

• To get to the decision, Biden had to move past residual tensions and make peace with a fierce primary competitor.
• The decision elevates Harris among the next generation of Democratic leaders and could give her a big advantage in 2024, if Biden were elected and decided not to run for a second term.

Between the lines: The pick gives Biden a running mate with strong prosecutorial skills, as Harris has proven at Senate hearings and during her strongest debate moments. That could help them make the case against Trump in the fall.

• But some Democrats will be watching her political skills closely, after her presidential bid fizzled and a New York Times piece depicted a campaign full of bad decisions and backbiting.
• She has also faced public and private questions from some Democrats about whether she'd be too focused on running for the presidency again, although other Democratic operatives have said the questions about her ambitions have been sexist and inappropriate.

The backstory: Harris, who at 55 is more than 20 years younger than Biden, is a former prosecutor and has been a senator from California since 2017.

• She solidified her national profile when she grilled Trump administration nominees and administrators, including Brett Kavanaugh during his Supreme Court confirmation hearing in 2018.
• President Obama recognized her talent early on, in 2013 famously calling her "brilliant," "dedicated" and "tough."

She had been seen as a front-runner when she announced her presidential campaign in January 2019, but she was never able to capitalize on the early momentum — except for a brief spike in public attention after her confrontation with Biden over federally mandated school busing at a June debate.

• Harris dropped out of the race in December, saying she didn't have the funds to continue.

As a presidential candidate, Harris campaigned on a $500-a-month tax credit that she called "the largest working and middle-class tax cut in a generation." She started out as a supporter of Medicare for All, but then switched to an alternative that would have preserved a role for private insurance.

• In an October interview with "Axios on HBO," she explained her decision: "I heard from people, 'Kamala, don't take away my choice if I want a private plan. Please don't take away my choice.' And I said, you know what? That is fair."
• "I said to my team, I know we're going to take a political hit for it. ... I knew I'd be called a flip flopper for that."
• She also said in that interview that "of course" it's different to run for president as a Black woman because in Americans' experience there is "not a reference point for who can do what, there is a lack of ability or a difficulty in imagining that someone who we have never seen can do a job that has been done, you know, forty-five times by someone who is not that person."

Harris has also faced some criticisms based on cases she argued and policies she enacted as California's attorney general:

• She defended the death penalty as attorney general, despite being personally against it.
• She didn't take a position on Proposition 47, approved by voters, that reduced some felonies to misdemeanors.
• She opposed a bill that would have required her office to investigate police shootings.

Reality check: It will be Biden who sets the policies if he wins — but Harris's record will be relevant if she's elected vice president, especially if she takes ownership of specific issues and projects as Biden did when he was Barack Obama's vice president.

• It will be also be relevant to her own political future.

What's next: Harris's speech accepting the nomination at the Democratic convention will be her chance to introduce herself to an audience of general election voters — and to show how well she and Biden will be able to work as a team.

• Harris will join Vice President Mike Pence on Oct. 7 in Salt Lake City, Utah, for the first vice presidential debate of the 2020 cycle.

Go deeper: Kamala Harris on the issues