No departing president has been more prescient than Dwight D. Eisenhower, a consummate soldier-statesman, in warning his fellow citizens:

“We must guard against the acquisition of unwarranted influence, whether sought or unsought, by the military-industrial complex.”

He cited “the potential for the disastrous rise of misplaced power” from this “immense military establishment and a large arms industry” and cautioned Americans that “we must never let the weight of this combination endanger our liberties or democratic processes.”

Fast-forward nearly 50 years, and here we are: a generation beyond being bogged down in Vietnam yet stuck interminably in the twin tar pits of Afghanistan and Iraq. But how, despite the alert by Ike, did we get here?

The incisive Pulitzer Prize-winning historian Garry Wills has written “Bomb Power: The Modern Presidency and the National Security State” to offer an answer.

What he finds is that our culture of government secrecy, muscular foreign policy and virtually unbridled presidential prerogative regarding military force grew from the way we ended what Studs Terkel called “The Good War.”

Wills writes that it was the Manhattan Project, the ultrasecret development of the atomic bomb, that began America’s dark dance with ultimate weaponry and the concept of president as sole arbiter of its use. Eventually, we even watched our country go to war pre-emptively, by choice rather than necessity — war that has not only begun to seem endless, but that has been waged against an abstract noun: “terror.”

When a president can bypass Congress and “set up an alternative justice system, secret and unaccountable, to ‘fight terror’ ” by essentially proclaiming a “permanent emergency” and “start a war on his own say-so,” Wills asks, “what can he not do?” That, in a nutshell, is what Wills sees as the morphing of America into a “National Security State.”

With the likes of James Madison and other Founders left to spin in their graves, Wills laments: “It is common now for a President to preclude action by Congress for the sake of an option he personally prefers.” Or to manipulate Congress into issuing blank checks—the Tonkin Gulf Resolution for one — that fall short of formal declarations of war. Precedent, then, builds upon precedent.

Although the Constitution specifies that it is up to the legislative branch to declare war, it has not done so since 1941-42. “Executive power,” Wills contends, “has basically been, since World War II, Bomb Power.”

It is the president who is followed by a military aide carrying “the football,” the 40-pound Zero Halliburton metallic briefcase containing the codes to launch a nuclear attack. And it is the president whose finger is on “the button.” As a result, Wills says, the Oval Office has accumulated power — and created an aura — far beyond constitutional intent.

Wills mentions a White House memo from 2002 referring to the Geneva Conventions as “quaint” and “obsolete” and wonders whether we’ve reached the point where those same two words might now be applied to the Constitution itself. To quote Madison, “No nation could preserve its freedom in the face of continual warfare.”

What makes Wills’ analysis all the more thought-provoking are examples of how some ideologically influential White House and Justice Department lawyers, emboldened by a like-minded vice president, had furthered the theory of the “unitary executive.” In essence, it condones giving the president, as “Commander in Chief,” carte blanche in using the military, ignoring international law, presuming guilt, torturing suspected terrorists, incarcerating open-endedly without due process, and intruding into the lives of private citizens without probable cause or court order.

Members of Congress may hold the power of the purse, but their leverage gets neutralized by fear of being labeled “soft on terror,” even unpatriotic. Outsized spending by the Pentagon is deemed sacrosanct, an article of faith. And in wielding American might, a president—except at election time — answers to no one.

Hardly what the Founders had in mind.

Then there’s “Information Power,” the executive branch’s misuse of secrecy, to which Wills ascribes four principal motives:

Embarrassment cover.

Congress deceiver.

Policy disabler.

Crime concealer.

When cornered, cry, “Executive privilege!”

Which brings us back to the military-industrial complex, a cornucopia of campaign cash for those seeking federal office. Including the presidency.

And could anyone from Madison to Eisenhower have envisioned our now severely overextended armed forces being augmented to such a great degree by paramilitary contractors such as Blackwater (whose notoriety has caused a name change to Xe)?

“We must guard against. . . .”

“Bomb Power” makes a convincing case that we haven’t.

Gene Krzyzynski is a veteran copy editor for The News.