The Democrats control Congress. If Obama gets elected president, the Dems will have no difficulty in authoring, sponsoring, voting out of committee to the floor, and finally passing a bill, which Obama will then sign into law. An Obama presidency will also see the appointment of several liberal Supreme Court justices, who will likely shift future Supreme Court decisions in favor of liberalism for decades to come.
Anti-gun laws could be enacted, challenged, and Constitutionally upheld by the Supreme Court under an Obama presidency, further anchoring gun control into our society.
Think of Obama as a trojan downloader for the soros virus.