When Sen. Robert Kennedy stunned the political world in March of 1968 with his bid for the Democratic presidential nomination -- after saying for months he would not run -- he said he was doing so "not merely to oppose any man but to propose new policies."

Everyone knew that Bobby disliked President Lyndon Johnson. Johnson's Vietnam War policy and his War on Poverty both showed little progress, but Kennedy seemed incapable of committing to running -- until Sen. Eugene McCarthy showed in New Hampshire that Johnson was deeply vulnerable. Four days after the primary, Kennedy was a candidate, promising a change in priorities, a change in leadership.

Vice President Joe Biden has said he is wrestling with the idea of running for president. But unlike Kennedy, Biden would not run to necessarily oppose Hillary Clinton, nor would he propose a drastic break from her, or President Barack Obama's, policies. Despite growing Democratic anxiousness over Clinton's email server problems, Biden and Clinton have a good relationship, predating their service on the Obama cabinet. Biden has not commented on the email controversy, and Clinton has called for giving him time to decide.

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They have not always been on the same page on policy matters -- he came out in favor of same-sex marriage at a time she was still opposed to it (and while Obama was still peddling his "evolving" viewpoint). And Biden is far less aggressive than Clinton on foreign policy issues. But that's not thought to be part of his consideration.

So why run?

The decision is not about foreign policy, or gay rights, or the price of milk. It's about a man who has served his nation with distinction, first with 36 years in the Senate and now seven years as an influential vice president. He has done everything asked of him, and more, and the logical next step is the Oval Office.

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In fairness, not everyone saw him as presidential material. There has been a steady rolling-of-the-eyes response to some of his antics over the years -- including uninvited backrubs, and gaffes that have earned him a "Crazy Uncle Joe" moniker. And in early polls, he has been well behind Clinton. The message seemed to be: "Thanks Joe, for all your service. You have won and earned our respect for your many accomplishments. But don't let the door hit you on the way out."

But now there is a sympathy factor to consider. He has suffered unfathomable losses in his personal life, most recently the death of his son Beau in May. The nation mourns with him. Yes, he made two presidential bids in his career, but both ended with little fanfare, in 1988 and 2008. Now there are the reports that Beau, and Biden's other son Hunter, pleaded with him to make one more run for the top job. That has fueled the 2016 candidacy speculation.

It's hard to see how he can succeed, given Clinton's money, staffing, early start and opportunity to make history -- let alone the inroads Sen. Bernie Sanders (I-Vt.) has made with the party's progressive wing. And although there is worry over Clinton's email server problems, Biden is not about to run because of that.

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It would be fascinating to see him try, though.

Mr. Completely Unfiltered vs. Ms. Totally Scripted. Political junkies, many already suffering from Clinton fatigue, are hoping he gets in. But that's a selfish reason.

Biden needs to do what's best for him and his family. In the end, I guess, he bows to reality, doesn't run for president, and leaves public life with the best wishes and gratitude from all of us.

Ken Rudin covered politics and elections for ABC News and National Public Radio. He hosts "The Political Junkie," a weekly radio podcast.