If you want to get into the statistics of how campaigns and publicity can game these, then we need to discuss the possibility of using ranked voting. This is where each person ranks all choices they are willing to accept in the order of their preference. If the votes are counted and their first choice has no chance (e.g. Paul), only then does their second choice get used instead (e.g. Romney). This eliminates the problem of scaring republicans that Obama might win if they voted Paul so they vote Romney to avoid splitting between Paul and Romney.
As one might guess, this requires the vote choices, the ranking and who that 2nd choice followed to be figured out. If more than 2 choices (should be unlimited, really) are allowed, then it would take a computer to calculate the top pick. Fortunately, just like the proposed voting system, this also can be done by everyone to compare accuracy and find manipulation.