This mix of powers has raised the issue many times in history of the ability of the President to engage in military action abroad without a formal declaration of war from Congress. It is clear that a concurrent resolution (a resolution passed by a majority of both houses) granting authority to the President to take military action is sufficient, as happened prior to the commencement of the Gulf War in 1991. But the President has used American troops several times in history without going to Congress for a declaration of war, and it was largely the result of the President leading and Congress following that the United States became involved in the Vietnam War.