Problem is, he knows that only a tiny fraction of those millions care enough about the issue to base their votes on it. He also knows that when push comes to shove even most of us die-hard 2nd Amendment supporters won't vote for a hard-core gun-grabbing Democrat.
True, there are 70-80 million people in America who own guns. But for most of them it isn't a major issue. As long as 95% of gun owners care more about pocketbook issues and/or party loyalty than they do about the future liberty and freedom of their children and grandchildren, our 2nd Amendment rights will continue to be whittled away.
I'm 65 so I won't be around to see it happen, but I would bet that within 25-30 years U.S. gun laws will be the same as the UK's are now.