Aftab Pureval, a Democrat seeking to unseat a Republican congressman in Ohio, knows the political risks in calling for gun restrictions – and taking on the powerful National Rifle Association, which has spent more than $115,000 supporting his opponent over the years.

Thirty-eight of the 59 Democrats backed by the party's "Red-to-Blue" campaign – targeting vulnerable Republican districts – have supported gun restrictions in their official platforms, a review of campaign websites shows.

At this point in the 2016 election cycle, only four of 36 Red-to-Blue candidates backed gun limits in their platforms, according to a Reuters review of archived campaign websites.

In 2014, the last midterm election, the NRA reported $27 million in independent spending to back candidates who oppose gun limits, compared to $8.6 million by gun-control groups, according to the non-partisan Center for Responsive Politics.

This year, a different voter bloc could help Democrats flip the 23 Republican seats needed to take control of the House: educated, suburban women who might normally lean Republican but see gun violence as increasingly personal, said Stuart Rothenberg, an analyst with the nonpartisan website Inside Elections.

In California, candidate Gil Cisneros has criticized Republican leaders for taking the gun lobby's "blood money".

...