Since the beginning of the last century, there have been 21 Vice Presidents:
Charles W Fairbanks
James S Sherman
Thomas R Marshall
Charles G Dawes
John Nance Garner
Henry A. Wallace
Harry S. Truman
Alben W Barkley
Richard Milhous Nixon
Lyndon Baines Johnson
Spiro T. Agnew
Gerald Rudolph Ford
George Herbert Walker Bush
J. Danforth Quayle
Albert Gore, Jr.
Six of those have went on to become the President -- three involved the death of the sitting President.
1) Coolidge replaced Harding after Harding suffered a heart attach while in office (1923).
2) Truman succeeded FDR after his death (1945) and was elected to a second term.
3) LBJ succeed for JFK after his assignation (1963).
4) Nixon was elected twice and resigned during his second term (1974).
5) Ford was never elected to be president or vice-president but instead took office upon the resignation first of Spiro Agnew and then of Richard Nixon (1974)
6) GHW Bush was elected twice.
The purpose of the VP, despite the recent advisory role some VPs have assumed, is to take over the presidency if the president dies or is unable to perform his/her duty.
The media over-blows the role the VP has in presidential politics. The media waited with baited breath for Obama to announce Senator Joe Biden (DE) as his running mate and McCain announcing Governor Sarah Palin (AK). Boring.
Obama selected a Washington insider. McCain an outsider. Biden has been dismissed in all his president bids. Palin has never sought nor held a national office. She relatively unknown.
Biden has plenty of experience; Obama has very little. McCain has plenty of experience; Palin little. The key items we should base our presidential vote on this November are:
Size of government
Taxes (capital gains, dividend, income, inheritance, new)
What these recent VP nominations have said to me is: Obama says one thing and does another -- wants change but sticks with status quo; and the liberal left is not concerned with equal rights or opportunities for all, they just care about promoting the liberal agenda.
Obama and Biden are flaming libs; McCain and Palin, though not my favorite ticket, are closer to the conservative agenda than not, especially Palin.