In 2014, 4,500 midterm ads promoted gun control. This year, more than 100,000 have already.

The mass shootings of the past few years may not have led to any major national gun policy changes. But gun control is playing a massively larger role in campaign advertising for the 2018 election than it did in the last midterm cycle. While mentions of gun policy have increased across the board, a Wall Street Journal analysis published Tuesday shows, ad mentions supporting stricter gun control policies have spiked dramatically. In the entire 2014 election, the Journal's data counts just under 4...