Now that Joe Biden is the official nominee for Vice-President from the Democratic Party, there’s no doubt that large numbers of the country woke up from their slumbers Saturday morning, turned on the television, and simultaneously asked themselves the same question: “Joe who?”

The bulk of the commentary, as is naturally the case in vice-president selection, is the politics of the thing. Whether it’s using the choice to criticize the Presidential candidate, give a quick bio of the VP nominee, or what this means about the Presidential candidate’s thinking, the focus is always on one thing: the politics of the choice. The questions are focused almost completely on how the vice-presidential selection will affect the election. No doubt the same thing will happen once McCain announces his nominee. The problem is that this singular focus is a mistake.

There’s no question that analyzing the politics of a VP selection is an important function, and the selection of a VP definitely helps provide some insight into the thinking of a Presidential candidate. And it’s only natural that the focus be on the campaign politics, as disrespect for the office of the Vice President an American tradition that started with the first Vice President, John Adams. Upon being selected for the office, Adams famously said that “[m]y country has, in its wisdom, contrived for me the most insignificant office that ever the invention of man contrived or his imagination conceived.”

Despite the distinguished Mr. Adams’ opinion to the contrary, the Vice Presidency is a significant office. The Vice President is, as the old cliche goes, “one heartbeat away from the Presidency.” That’s not just a saying, either. It’s the truth. Every Vice President is a potential President. Accordingly, the most important analysis to make after the announcement of a Vice Presidential nominee is not, “how will this play in the swing states?”–it’s “would this person make a good President?”

This is not an idle question. Nine Vice Presidents have ascended to the Presidency because of death or resignation. Most of these Presidencies were a pretty mixed bag.

In 1841, John Tyler was the first Vice President to succeed to the Office of the Presidency after William Henry Harrison died from pneumonia. His Presidency is widely regarded as a disaster which exacerbated regionalism and helped fuel the fires of the issues that would lead to the Civil War. He was also the first President against whom members of Congress attempted to pass articles of impeachment against. Less than a decade later, Millard Fillmore ascended after Zachary Taylor’s death, and was famous for singing the Fugitive Slave Act.

In 1865, Andrew Johnson became President after the death of Abraham Lincoln, and went on to lead the country through what virtually all historians recognize as one of the worst presidencies ever. Johnson would later become the first President to have articles of impeachment brought against him. (Although, it’s worth noting that Andrew Johnson had articles brought against him for violating a law he believed to be unconstitutional. The Supreme Court would later rule that same law unconstitutional.)

Other Vice Presidents who ascended to the Presidency after the death of the President were Chester A. Arthur, whose major accomplishment was a bill stopping Chinese from immigrating for ten years, Lyndon Johnson, who started the Vietnam War, and Gerald Ford, who used the powers of his office to pardon Nixon of his crimes.

Not that all Vice Presidents who ascended to the Presidency were bad Presidents. Theodore Roosevelt is widely regarded as one of the most successful Presidents of all time, and Roosevelt became President after the assassination of William McKinley. Calvin Coolidge and Harry S Truman are also generally regarded as successful Presidents. The point, though, is that a Vice President becoming President is hardly a rare thing in American history–which is all the more reason to scrutinize the VP nominees for more than just whether they’ll attract particular voter demographics.

It’s also worth mentioning that the death or resignation of the President is not the only way in which the Vice President can exercise the powers of the President. Richard Nixon served as acting President during the Eisenhower Administration to fill in while Eisenhower recovered from a heart attack. For this and other reasons, the 25th Amendment was adopted, which provides for the Vice President to serve as President in the case of incapacity. Since the adoption of this Amendment, George H.W. Bush and Dick Cheney have served as Acting President under the 25th Amendment.

History teaches us that despite the levels of disrespect typically heaped on the office of vice president, the fact remains that many Vice Presidents have gone on to become President themselves, either through succession or through incapacity. Accordingly, the most important question to ask about any vice presidential nominee is not about whether he “balances the ticket” or “helps the campaign narrative.” The most important ask about a vice presidential nominee is simply this:

If something happens, would he make a good President?