As a presidential candidate, Sen. Kamala D. Harris (Calif.) fell short of the high expectations that greeted her electrifying entry into the 2020 race for the Democratic nomination. She didn’t even make it as far as Iowa.

But the qualities that hampered her when she was running in her own right could be what make her ideal as former vice president Joe Biden’s running mate — and ultimately, as his partner in governing the country as it struggles to recover from the devastation wrought by the novel coronavirus.

Harris brings to the ticket and potentially the White House the thrill of history as the first Black and Asian woman to be put forward by a major political party as a national candidate.

She had from the beginning been considered the front-runner on the list of a dozen or more qualified women said to be on Biden’s shortlist. (I should disclose here that my adult son works for the Biden campaign.)

There is an echo here of Biden’s own selection in 2008 to share the ticket with Barack Obama. Biden, too, was a onetime adversary who proved more effective as a wingman.

Harris has often been criticized at various stages in her career for being too cautious and deliberate. But those are just what a running mate should be. Harris is unlikely to make any big mistakes. And in the high-stakes moment that will count the most — her Oct. 7 debate with Vice President Pence in Salt Lake City — she can be relied upon to shine.

No one who saw her scorching interrogation of Attorney General William P. Barr when he testified before the Senate Judiciary Committee in May 2019 is likely to forget the methodical way in which she dismantled his implausible denials that he had undermined the investigation by special counsel Robert S. Mueller III into Russia’s interference in the 2016 presidential election.

Given the fact that Biden, if elected, will be 78 years old when he takes the oath of office next January, his running mate’s experience is likely to matter more to voters this year than it usually does — and there, too, Harris had the edge.

She represents the most populous state in the nation in the Senate and before that gained executive experience as San Francisco’s district attorney and then California’s attorney general.

As she put it last year in South Carolina: “I know how to take on predators. . . . So let me tell you, we need somebody on our stage when it comes time for that general election who knows how to recognize a rap sheet when they see it and prosecute the case.”

Harris has recently been dinged in the media for being “too ambitious” — as though any man who ever ran for national office wasn’t.

But as a candidate, she sometimes seemed the opposite. Harris sounded uncertain about herself — sometimes embracing her record as a prosecutor, for instance, and at others downplaying it.

She had plenty of far-reaching policy proposals, on issues from teacher salaries and gun control to taxes and equal pay for men and women. They never, however, added up to a clear vision or a rationale for her candidacy. And she seemed ill at ease when called upon to talk about herself or her own life experiences.

I hope we see more of the Harris I got a glimpse of during the 2019 South Carolina state party convention, when she spoke about her raw childhood memories of racial discrimination.

Harris recalled how it stung to see people “looking down” on her Indian American mother, a medical researcher, “assuming that she was somebody’s housekeeper and treating her like she was a substandard person because of assumptions of who she is based on how she looks.”

Later, I asked her why she so rarely shared personal reflections such as these. “It’s in me. Everything you heard today is in me,” Harris told me. But she added: “It doesn’t come naturally to me to wax on about who I am.”

The country is about to get to know her a lot better, but both she and Biden know that the most important quality in a running mate is how well her choice reflects on him. In Harris — a onetime opponent — Biden has picked the surest and safest bet.

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