If you keep up with the national news then you are aware of of the growing rift between the Obama administration and Israeli
Prime Minister Benjamin Netanyahu. This rift has been growing for six years. The primary cause of the rift is that the US has taken a less hard line toward Iran's nuclear ambitions and Israel fears for its survival if Iran becomes a nuclear power. Other issues that have caused tension is that Israel continues to allow Israeli settlements in the territory that is often referred to as Palestinian territory.
The tensions between the two leaders has lead the Obama administration to engage in efforts to defeat Netanyahu in his upcoming election for another term as Prime Minister of Israel. Obama is funneling money to Netanyahu's opponent.
Once the Republicans gained control of Congress, they invited Mr. Netanayahu to address a joint session of Congress. It is assumed Mr. Netanyahu will speak on how a nuclear armed Iran will cause greater nuclear proliferation in the Middle East, lead to further destabilization in the region, and why a nuclear armed Iran is viewed as a threat to Isreal's survival.
It is not unprecedented that a foreign leader addresses the U.S. Congress. Numerous heads of state have addressed Congress over the years. Congress is a co-equal branch of government with a role to play in foreign affairs. Congress must approve the budgets necessary to fund our diplomatic efforts, must fund the defense budget, must approve ambassadors, and has the constitutional authority to declare war. Certainly Congress is not overstepping any bounds by inviting a foreign leader to address the body. The President is livid, however, and has let it be know that he objects to Netanyahu speaking to Congress.