How important are national polls in American Election?

How important are national polls?

It's a tough task to gauge the mood of a nation that is home to more than 300 million people, but that doesn't stop the pollsters from trying.
National polls tend to have a sample size of about 1,000 people or more and can track movement and general opinion pretty well.
But the US election is won and lost in swing states and decided by the electoral college system (What is the electoral college?).
This means that polls in states that look like they could vote for either candidate (Florida, Ohio and Pennsylvania to name just a few) play an integral role in election projections.
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What are the polls like in battleground states?
We've identified 13 states that can be considered battlegrounds in this election.
The map below shows them and which way they're likely to vote based on data collected by polling resource website Real Clear Politics.
Map showing which candidate is ahead in each of the battleground states
If those states stay the same colour (blue for Clinton, red for Trump) through to election day - and both candidates win the remaining states they are expected to - it would be a clear victory for Hillary Clinton.
For Donald Trump to have a chance, he needs to turn Florida and Ohio red and win a few others too. As it stands, while Trump is just edging Ohio, Clinton leads by a small margin in Florida.