On reading polls for the U.S. election, the first thing you need to remember is to ignore the national polls. Because of our rather convoluted method of election, the overall national number is of only indirect importance. What matters is the state-by-state results. A good place to get a better feel for that is the electoral vote site, which tallies the most recent individual state polls.
Forgive me if this is overly pedantic, but for those outside the U.S., here’s how our screwy election system works.
The actual election of a president doesn’t happen via national popular election. Instead, each state sends a group of “electors” to an “electoral college” following the election. The candidate who wins a state’s popular vote wins all of the state’s electors. So when Al Gore, for example, won New Mexico in 2000 by the tiniest of fractions, he got all five our our electoral college votes. Totalled up across the country, this is how George W. Bush won the presidency despite getting fewer total votes nationwide than Al Gore.