Put the focus on adopting regulations at a state and local level where such legislation has broad popular support. Since the market for guns operates on a national level, this isn’t an idea approach, but it is politically viable.
Continue to press the GOP for federal legislation to keep guns out of the hands of potential terrorists. It won’t pass, but the issue will resonate in the 2016 campaign.
Try to show more public sympathy for rural gun culture. The Democratic Party is cratering in rural areas that don’t contain national parks and ski resorts–this could help a bit.