If a security threat is deemed drastic enough to declare war, which of the following is able to make that declaration? Congress Senate president House of Representatives

Congress is allowed to declare war.

If a security threat is deemed drastic enough to declare war, the Congress is able to make that declaration.

This is one of the enumerated powers of Congress. Among others, Congress shall have the power to raise and support armies, to coin money, to declare war, etc.

Congress had declared war on eleven occasions in American history, Against Japan, Germany, and Italy, Bulgaria, Hungary, and Rumania, etc. The last was in World War II.