In the debate over whether Congress has the power to shape war policy, "the president's challengers have history on their side," writes Julian E. Zelizer, a professor of history at Boston University. The legislative branch has often played a significant role in wartime politics, he says.
Mr. Zelizer points specifically to Congressional efforts to end the Vietnam War. During that conflict, he says, lawmakers "forced discussion of difficult questions about the mission, publicly challenged the administration's core arguments, and used budgetary mechanisms to create pressure on the Pentagon to bring the war to a halt."

As an example of such efforts, he cites the Senate Foreign Relations Committee's 1966 hearings on the war. The televised hearings, led by Sen. J. William Fulbright, Democrat of Arkansas, "stung" President Lyndon B. Johnson, Mr. Zelizer writes, because it was the first time Americans were able to watch top administration officials testify about the war. Senator Fulbright used the hearings, the author says, to insist "that there was no need to escalate operations in Vietnam because the conflict did not involve the vital interests of America and could easily be a 'trigger for world war.'" The hearings, he adds, "helped give antiwar protest a certain degree of legitimacy" and "also ensured that the mainstream media covered criticism about the war."

Congress was able to exert further control over the war, he writes, by using "the power of the purse." On three occasions, he notes, President Richard M. Nixon was forced to accept legislation that essentially stipulated how war dollars could be spent. ...