Can we trust the presidential polls? 

Polls have both increasingly shown Democratic presidential candidate Hillary Clinton expanding her lead by as much as 12 points nationally while Republican presidential candidate Donald Trump has blasted the polls as biased.  

FiveThirtyEight.com gives Clinton an 84.3 percent chance of winning the presidency. 

But can the polls be trusted? 

CNN's Tom Foreman examines the issue in the video below.