Picking a running mate is the first big test of a potential president's decision-making skills. Joe Biden aced that test on Tuesday. His selection of California Sen. Kamala Harris is at once historic — the first woman of color on a major party's national ticket — and one of the safest choices he could have made.

As a former prosecutor who has long worked within the system, Harris wasn't the first preference of hard-left Democrats. And that's exactly the point: Even in making this groundbreaking choice, Biden has once again shown the steady, moderate instincts that will contrast well with the incompetence and recklessness of America's current president.

Harris, 55, is the daughter of a Black Jamaican father and an Indian mother, both immigrants. She was a prosecutor in San Francisco, a district attorney and a two-term California attorney general. She was elected to the Senate in 2016 and was briefly the front-runner for the 2020 Democratic presidential nomination.

In the Senate, Harris has been a strong (but not radical) progressive, and a forceful challenger to the worst abuses of the Trump administration, especially on immigration. From her seat on the Judiciary Committee, she has been a leading critic of Attorney General William Barr, exposing his campaign to mislead the nation regarding the Russia investigation.

On the campaign trail, her tough-on-crime record as a prosecutor drew opposition from progressives. Was it their preconceived notion that a Black woman prosecutor should be soft on crime?

There's a difference between blindly supporting the police, no matter what, and supporting responsible law enforcement. All indications are that Harris falls squarely into the latter camp. She is well positioned to provide a credible counterweight to some Democrats' reckless "defund the police" rhetoric, which is both bad policy and bad politics.

The elevation of a Black woman to national office could, in itself, provide a measure of national healing in these fractious times. Anyone who scoffs about identity politics might want to consider the first and still most-common example of that phenomenon: All but one president and every single vice president have been white males. It's past time for an administration whose identity looks more like America.

President Donald Trump is already trying to capitalize on Harris' primary campaign attacks against Biden. The fact that Biden recognized Harris' debate performances as a sign of strength, even when she targeted him for a withering attack, is a tribute to Biden's judgment and character — in sharp contrast to Trump's petty vindictiveness.

Crucially for the running mate of a man in his late 70s, it's easy to imagine Harris stepping up to the presidency if the need arises. In the meantime, her selection should stand as further proof of Biden's solid fitness for office, as he seeks to unseat the most dangerously unfit president in America's history.

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