The rise of television has change our selection process. 25 years ago, candidates had to go through a rigorous selection process which involved lots of campaigning and refinement of the platform to meet the needs of the party and constituency. Normally several candidates established there worthiness and the primaries remained a viable step in picking out the single best qualified candidate.
Today, the candidate is usually "chosen" way before the primaries are done. States like New Hampshire that have early primaries tend to pick the presidential candidates, because it is though whoever takes the early lead has the momentum. Why has this changed? People see the results of early primaries on TV and assume that candidate is going to hold his lead, and usually don't rally around a underdog candidate to oppose the early leader. Secondly, with the advent of TV, people get to see what the candidate looks like. Nixon was thought to have lost the presidency to Kennedy because of the televised debate in which Kennedy looked better than Nixon, even though those that heard the debate on radio strongly favored Nixon's answers. It has been shown that looks and appeal have as much to do with the selection of candidates for presidency as political prowress and experience. Bush looked the part, fell in with the party line, and road the coattails of his dad right into the Republican nomination. Also, candidates with any spec on their past history are eliminated early on because the media tends to focus on dirt on candidates rather than qualifications. So if you have a candidate that is very well qualified but has any blemishes in his past, he will not be chosen over the inexperienced candidate that has a clean record.
It is widely believed by many political experts that Gore was better at debating and arguing his platform than Bush in the presidential race. But Gore looked stiff on television, and many experts believe that is what caused him to lose a very closely contested battle.
This is all supported by the govt. class I took last semester where we examined changes in the political process.