An overused cliché in American politics is that the Vice-President is only a heartbeat away from the Presidency. But, that's real.
And, yet, we have an amazing recurrence: Too often the person that the Presidential nominees select for their running mates is a political or intellectual nonentity, or someone with no proven track record. Take 1996, 2000, 2004, and 2008 as examples. We were subject to having the following choices: Al Gore or Jack Kemp, Dick Cheney or Joe Lieberman, Dick Cheney or John Edwards, Sarah Palin or Joe Biden. Deuces are apparently wild.
The process is at fault. Unless the candidate is running for a second term (like Obama this year), the potential pool of running mates also included persons who ran for president against the candidate, and gored the nominee in the process. Also, the Vice_Presidential nominee is selected by the nominee personally to fit certain ethnic, regional, or other strategies. So they invariably go with relatively safe nonentities.
But nobody seems to deal with the reality: four of our Presidents were assassinated, and several have been to some degree incapacitated to some degree while serving. Woodrow Wilson comes to mind for sure; but others could be good bets as well.
Wouldn't it be better if the choice for Vice-President be left open at the Conventions? There's no guarantees; but maybe the delegates could come up with better choices.
Or, even better, we vote separately for the President and Vice-President, even if it means they might come from different parties. And why is that so bad?