President Obama has stated that he plans to accomplish some goals of gun control via executive order. Like many executive orders, it will be unconstitutional. President Obama is not the first president to issue unconstitutional orders, though he has become famous for his efforts to bypass Congress. The true purpose of executive orders is to direct the enforcement of Congressional legislation, but Article II of the Constitution, which establishes the executive branch of the government, does not mention the authority to issue orders with the force of law.
The purpose of the executive branch, regarding domestic policy, is to nominate and appoint certain government officials, and to direct the enforcement of laws made by Congress. Regarding legislative authority, the president may check the power of Congress by veto, and is encouraged to recommend laws to Congress. These recommendations must be passed by Congress before they become enforceable.
As mentioned earlier, President Obama is not the first president to issue unconstitutional executive orders. Many previous presidents are guilty of this breach of constitutional constraints. President Franklin Roosevelt, for example, is known for his 1933 order prohibiting the private holding of monetary gold, and for his 1942 order which forced Japanese-Americans into internment camps. These types of actions were not within the scope of legislative authority, much less executive authority. Some of the orders that make up the "We Can't Wait" initiative, however are consistent with delegated Congressional authority, but not executive authority. The framers of the Constitution delegated powers among the different branches in order that they may be best restrained. They knew that politicians with agendas, even agendas that are supported by a majority of the people, are dangerous for a republic.
The Constitution is clear that the only acts of the federal government which are enforceable against citizens are those which are made by Congress, pursuant to the delegated authority of the legislature, and either approved by the president or have sufficient support from Congress to override a presidential veto. Executive orders used to bypass Congress in the creation of law are not permitted by the Constitution.