The last time a VP pick was instrumental to a race was 1960, when Texas Democrat Lyndon B. Johnson helped put John F. Kennedy over the top by attracting votes from the South. There have been plenty of strong candidates and incredibly flawed VP picks since then, but none have helped determine the outcome of the presidential race. Put another way, John McCain didn't lose because he picked Sarah Palin in 2008, but it sure didn't help.

All of this is not to say the VP pick is not important. The decision -- once a means of finding ideological or regional balance -- is increasingly a test of the candidate's judgment and an early indication of the kind of administration he intends to run.

Bill Clinton, for example, was widely expected to choose someone from the more liberal wing of the Democratic party and not another son of the South. But by choosing Al Gore, he made a broader and bolder statement; this campaign was about generational change and a new style of leadership. Both Clinton and Gore were younger men in their mid-40s who brought more physical energy to the race than George H. W. Bush, then in his late 60s. The contrast fueled the narrative that America needed new, younger leadership.

More importantly, Clinton and Gore were comfortable with each other and shared the same basic world view. The same was true for Barack Obama and Biden and, for better or worse, Richard Nixon and Spiro Agnew.

Ultimately, the success of a VP pick comes down to these two factors: whether the two running mates share a genuine and comfortable partnership, and whether the VP reinforces the broad message about how the presidential candidate intends to govern.

So, what is Biden going to do? He has already made the kind of statement Bill Clinton did by picking Gore -- making generational change a centerpiece of the campaign. By committing to pick a woman early in the campaign, Biden signaled his intention to break the glass ceiling. Women are the key to Biden's election success, particularly Black women. This was an important message from the beginning, helping to blunt any unease within the Democratic party that Biden was just another old guy in the party.

Now the only question is: which woman? Judging from his experience with Obama, the former vice president will want to pick someone he's comfortable with -- someone he knows and trusts. Vetting the VP choice is one of the most consequential jobs of a fledgling presidential campaign. If the first rule of VP picks is to do no harm, the second rule is this: absolutely no surprises. Biden will want to avoid any unwelcome revelations such as we've seen in the past -- like Palin's much-mocked ignorance about international affairs and Geraldine Ferraro's husband's finances becoming a flash point when she announced he would not be releasing his tax returns.

Getting the vetting right is an important test of competency. And that's especially important in this election cycle. Biden is running as the candidate who won't make the mistakes the Trump adm