Republicans could be pro active and in the House, pass a bill that says the rights of American gun owners will be protected including defense weapons such as the AR 15 and the 30 round clips they came with.
I am not comfortable with allowing Congress to define the scope of our rights. A better solution might be to let Congress rule where it has legitimate power - they can define the general militia to be all men and women over the age of 18 who are not felons, and addressing the "well regulated" part, Congress can define the AR-15 or similar platform as the standard weapon for the general militia.
You have the 2nd Amendment right to own any other arm you feel you'd like or need, but you have the duty to keep an AR as part of the general militia.