This post on FiveThirtyEight is worth calling out for being sensationalist and linkbaitish, if you ask me. 

Harry Enten says that Trump is just a polling error behind Clinton.

I'm not questioning if it's factual, but imho it's unnecessarily alarming because:

• You can lose the popular vote and still win the election. Both campaigns if they're well-run, deploy resources according to whether or not it gets them more electoral votes. Gore won the popular vote in 2000, for example, but lost the election. Another way of saying it: A vote in Florida counts more than a vote in California or Wyoming.
• It doesn't take into account turnout. I've listened to their podcast, and they say that they don't know if turnout is baked into the numbers they use. Do Clinton votes count more in polls than Trump votes because she likely has a more effective turnout effort? They don't know what the polls they're basing their number on do re turnout.

Anyway, the goal is not to get the most votes, it's to get the most electoral votes. The number he's citing is popular votes. 

This post by Nate Silver in 2011 backs me up on this, btw. ;-)

PS: Before you rush to call me wrong, yes he does say it's the popular vote, but he doesn't appear to say that by itself it's a meaningless number.