To be honest about it, I recently took a political science course that focused on the many ways that Presidents, historically and currently, have increased the amount of power the executive branch has and ways that they have, again historically and currently, circumvented Congress. This is part of the reason that we've been in a lot of "conflicts" in the last seventy years but no "wars" since WWII. Policy statements, executive orders, signing statements, manipulating treaty signing privileges, use of executive agencies...there's a lot of ways to do it, and all of them have done it to some extent.
This is why libertarians want to strip the executive branch down to just what's in the constitution, and I can respect that (but I don't agree with it). There's such massive precedence for it at this point that it would take a constitutional amendment (in all likelihood) to even attempt to curtail it. You're seeing it as a problem with President Obama because you don't like what he's doing with those expanded executive powers, but everyone who's sat in that chair for the last hundred years has done similar things with their power and pretty much completely gotten away with it. There's no way that a policy statement, executive order, or anything of the like will result in impeachment. The Supreme Court has upheld examples of them as constitutional, including the controversial Japanese Internment executive order.