On the average, national polls show that Hillary Clinton will likely defeat Donald Trump in next month's election. Trump's response is familiar. "They are phony polls put out by phony media and I'll tell you what all of us are affected by this stuff and what they do they try and suppress the vote that way people don't go out and vote but we're winning this race. I really believe we are winning" But, from time to time, polls show Trump doing better. Some news media report there's a close race, and Trump can claim he'll be the eventual winner. So how's a prospective voter to know how the election is really going? Is political polling an art or a science? We talk to some leading practitioners about how they come up with numbers that can influence the ultimate outcome — whether they're right or wrong.