So far this cycle there's been more than $124 million spent on over 280,000 ads about immigration in House, Senate, and gubernatorial races, per CNN. That's five times what was spent on immigration-related TV ads in the entire 2014 midterm cycle.

Why it matters: Immigration doesn't show up as the number one issue in polls, but the ad spending by both parties suggests it'll be seared in voters' mind come Nov. 6. And both sides are hoping it'll energize their base.