One man, the president of the United States, has the power to send us to war — not constitutionally, but effectively.

Whenever the country is in danger from an outside power or is hurt, feels itself to be humiliated or made to believe it is threatened, the president can go to Congress on a wave of public excitement and get war-making authority.

When we hear presidential candidates such as Gov. Mitt Romney criticize a policy of “procrastination” with Iran — implying, go ahead and bomb the Iranians’ nuclear sites — it is good to bear in mind that he alone could send us to war.

“Hope is not a foreign policy,” declared the virtually certain nominee, Romney. “The only thing respected by thugs and tyrants is our resolve, backed by our power and our readiness to use it.”

What do these words — brave only in the context of an auditorium — suggest: that like Lyndon Johnson or George W. Bush, he would search for a minute or manufactured excuse for war with Iran?

In the general election campaign, perhaps a clearer picture will emerge of the temperament of the two candidates and of the trail of logic and evidence that would lead them to seek congressional approval for hostilities anywhere.

It is Congress that has war powers granted by the Constitution in Article I, Section 8, Clause 11, which vests in the Congress the power to declare war, in this antique language: “[Congress shall have Power...] To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water…”

That is what the Constitution says, and that is the straightforward process followed by Franklin Roosevelt in his “day of infamy” speech to Congress declaring a state of war with Japan, and three days later with Germany and Italy.

But our two most recent and unnecessary wars with Vietnam and Iraq were conceived in deceit, mangled at birth and led to widespread destruction and deaths of U.S. military and uncounted Vietnamese and Iraqi casualties.

The Gulf of Tonkin Resolution, which launched major combat operations in Vietnam, was based on the fictitious report of a second skirmish with a U.S. destroyer in far northern waters — an attack that never happened.

Excited congressmen passed the resolution 416-0.

A less excitable, longheaded view of the conflict was taken by George Kennan, the author of our “containment” policy that, with patient application of power under control, led to the downfall of the Soviet Union.

He told Congress that Ho Chi Minh was not Hitler; he wanted independence for Vietnam, not foreign aggression. Neither would he be a puppet of Beijing or Moscow, Kennan said.

Desire for independence was confirmed for me by a deputy foreign minister on my first visit to Vietnam. He said, “We have smelled Chinese (….) for a thousand years and been under a French heel for 50.”

Defeating Ho, however, would cost civilian lives, Keenan said, and suffering on a scale “for which I would not like to see this country responsible.” The toll of U.S. military alone was 58,151 dead, mainly young men in their teens and 20s.

As if he could foresee our interminable, costly and inconclusive Iraq and Afghanistan wars, he said America should not continue to “jump around” like “an elephant frightened by a mouse.”

A wiser standard would be that of John Quincy Adams: to sympathize with freedom everywhere; to fight for it only where feasible; and to “go not abroad in search of monsters to destroy.’

Kennan counseled that an orderly end of the Vietnam commitment would be the wiser course: “There is more respect to be won … by a resolute and courageous liquidation of unsound positions than by the stubborn pursuit of extravagant and unpromising objectives.”

Such wise counsel was available but unheeded as the Bush administration used stealth to build support in Congress for a war to rid Saddam’s Iraq of weapons of mass destruction … that did not exist.

Two days before the authorization by a large bipartisan majority for military action against Iraq, 75 senators were told that Iraq had missiles that would reach the East Coast, a “fact” doubted by many Pentagon and intelligence experts.

So, some eight years later we left Iraq having slain a monster, torn down and rebuilt some of what we tore down at a cost of more than $1 trillion, and with U.S. military casualties that could exceed that of the Vietnam War, according to some estimates.

As the Afghanistan adventure winds down and the presidential race heats up, it is worth bearing in mind that a president can start a war squandering American lives and treasure: which candidate will keep his cool and which one will go looking for monsters to kill.

H. Brandt Ayers is the publisher of The Star and chairman of Consolidated Publishing Co.