In general a politician has his best chance of getting a vote from his own supporters, and his second best chance from the other guy's supporters.
Neither candidate can count on nonvoters to be motivated to vote.
Sure, there'll be some ~ but the rule is going to be the same as I stated it ~ a vote for McCain was one less vote for Obama.
You have it a bit backwards, actually.
Yes, there are voters and non-voters.
But voters tend to vote for a particular party.
There is a certain ceiling on the number of people who vote, and non-voters are unlikely to be converted into voters. However, it can happen in rare circumstances.
However, voters can become non-voters. These are people who are not inspired by the candidates their party of choice has selected, or not motivated by the issues in the race.
And that is what happened with the GOP ticket in 2008.
Fewer Republican voters came out to vote than had 4 years earlier.
At the same time, more Democrat voters came out than ever had in any election in history. Many of these were non-voters who became voters for the first time. They were not voting for a party or a platform, but for an individual, because they wanted to be part of history by voting for the first black man to run for president. It was a feel good personal statement for them. That moment has passed, history has been made, and so many of them won’t be there for 0bama in 2012.