Joe Biden intends to name a woman as his running mate. Selecting that woman, however, is a much harder decision, almost certainly the most consequential he will make this year, revealing much about his values and his judgment.

We are already hearing the chatter: Should he choose a woman who can help him get elected because she represents a key swing state, a key ethnic group or an important region? Or should he select a woman who is steeped not only in politics but also in public policy with a proven record in public service who can significantly bolster Biden's ability to govern?

I believe Biden should focus heavily on governance, because it stems from his own experience as senator and vice president, and because rarely has a running mate had more than a marginal effect on the election outcome. And he must remember that he could well be selecting a future president. Some nominees, alas, apparently didn't remember, giving us Dan Quayle in 1988 and Sarah Palin in 2008, whom many saw as unqualified.

Biden should assume for these purposes that he will be elected and will immediately face the formidable fallout of the continuing coronavirus pandemic — the 1918 pandemic lasted until mid-1919 — and an unrecognizable economy with probable double-digit unemployment. Both crises will require new thinking, strong leadership, empathy and compassion.

He must also devote immediate attention to lessons learned, so that the issue of public health is elevated to the top of the nation's agenda. Accomplishing all of this will be a monumental task, and he will need the best talent available to help him, especially in his vice president, who must have the intellect, experience and confidence to advise and, when necessary, to disagree forcefully with him, because too few others will when the stakes are high and the atmosphere tense.

I was privileged 44 years ago to be present at the creation of the modern vice presidency, an almost total transformation of the nation's second most important office, which for nearly 200 years was derided for its irrelevance. As Walter Mondale's chief of staff in the Senate and then in the White House, I witnessed firsthand how he and Jimmy Carter reshaped a constitutional afterthought into a huge asset for the president. They decided Mondale would be an across-the-board adviser and troubleshooter for the president, focused heavily on furthering his agenda. To make this work, he would need unprecedented access to both the president and the White House paper flow, including classified national security information. Mondale proposed all this and more to President-elect Carter when we met with him at Blair House in December 1976. At Carter's request, Mondale sent a memo incorporating the conversation to the president-elect, who quickly approved it.

President Carter went further, offering Vice President Mondale an office in the West Wing, close to his own. He admonished everyone to respond to a request from the vice president as if it came from the president. He added that anyone found undercutting the vice president wouldn't be around for long. He made me a member of his own senior staff to help facilitate the integration of staffs. No one doubted that Carter was totally committed to this new arrangement, which was the primary reason for its success, yet he still has not received the credit he deserves for this important and lasting innovation.

Subsequent presidents and vice presidents took note, and most adopted, with appropriate variations, the Mondale model. In a sense it has become institutionalized through use; extralegal adaptation has effectively moved the vice president from the legislative branch of government, where he or she presides over the Senate, to the executive branch, where he or she can make a much greater contribution as a unique adviser to the president and become better prepared to assume the presidency if necessary.

After leaving the White House, I offered to explain the modern vice presidency to new occupants of the office of both parties or their top aides. Most heard me out respectfully, with particular interest in the weekly lunches in the president's private office where Mondale was encouraged to raise in confidence anything on his mind.

Vice President Dick Cheney invited me to have lunch with him and his aide Lewis Libby to learn about the Mondale experience. Libby asked most of the questions, Cheney almost none; he was so oddly incurious that I wondered why I was there. It later became apparent that he had his own understanding of the office, using it to establish his own national-security power center in the White House. He proved to be an outlier among modern vice presidents, whose unspoken mantra is "There's only one agenda, and it's the president's."

Viewing President Barack Obama's leadership style up close for eight years had much to do in shaping Biden's ability to actually be president if necessary. No one knows more about the office of vice president than Joe Biden. When he was elected, he had extensive conversations with his friend Walter Mondale. Biden and Obama worked out their own relationship based on the by-then established principles of the modern vice presidency, adapted to reflect Obama's needs and Biden's strengths. It's unlikely President Obama had been much impressed with Biden's brief foray into the 2008 presidential contest, but he was probably very impressed with his performance in the Senate during the two years they overlapped, especially on the Foreign Relations Committee. Blending Biden's legislative skills and knowledge of foreign policy with Obama's deficit in both areas was a wise move. Obama had the self-awareness to know what he didn't know and the wisdom to seek it in someone he wanted close by.

Biden has said he wants a vice president with whom he is "simpatico," presumably meaning someone with whom he is both personally and politically compatible and who can be trusted to help him both campaign and govern. This intangible element is by far the most important factor in the equation, and it should be decisive. The best politics for Joe Biden will be the selection of a woman who will be, and be seen as, qualified to be president of the United States.

Richard Moe was chief of staff to Vice President Walter Mondale and a member of President Jimmy Carter's senior staff from 1977 to 1981. He is the author, most recently, of "Roosevelt's Second Act: The Election of 1940 and the Politics of War." He wrote this article for the New York Times.