Barack Obama has "dramatically expanded" the notion of when presidents can use force without permission. He has left "an extraordinary legacy of war powers." History will assign far more importance to these precedents than we do. They make it significantly easier for future presidents to wage war unilaterally.

Those may sound like the concerns of an anti-war activist. In fact, they're the conclusions of Jack Goldsmith, who led the Office of Legal Counsel for part of the George W. Bush administration. He isn't someone with a narrow understanding of executive power. But in a recent speech, he cited three specific ways that Obama expanded the war power beyond anything attempted by the Bush administration.

The three precedents are as follows:

1) Article II, Section 2 of the Constitution declares, "The President shall be commander in chief of the Army and Navy of the United States, and of the militia of the several states, when called into the actual service of the United States." Almost everyone agrees that this gives the president the power to repel an attack on America. President Bush argued it empowered him to preempt imminent threats.

(Read More: Obama To Ask Congress for New War Powers To Fight ISIS)

Obama has gone a step farther.

He cited his Article II authority to justify waging war in Libya, a "pure humanitarian intervention" with "no conceivable self-defense rationale." And while he did not bomb Syria after its regime used chemical weapons, he argued at the time that Article II empowered him to take action unilaterally in order to "protect regional stability" and "enforce international norms," a standard that would permit an incredible variety of unilateral wars. As Goldsmith put it, "to decouple the use of force in such a clear way from self-defense" is a sweeping change.

2) The War Powers Resolution is a statute passed in the aftermath of the Vietnam War that limits how long the president can wage war without an act of Congress. There is debate about whether some of its provisions violate the Constitution. But the Obama administration has always insisted that it is binding law.

The law declares that the president must cease "hostilities" after 60 days without congressional authorization. In Libya, Obama waged war beyond that two-month period. The legal theory he put forth to justify that apparent breach of the statute?

"He basically said that the seven-month war from the air, which decimated Libyan forces, which killed hundreds and hundreds of people, which removed a leader from power, didn't count as 'hostilities,' and therefore the statute just wasn't implicated," Goldsmith said. By that logic, future presidents could order bombing raids for months, kill hundreds, and change regimes without ever going to Congress, so long as the war was waged from afar without "boots on the ground."

3) What's colloquially known as the War on Terror is fought under legal authority provided by the authorization to use military force, or AUMF, that Congress passed in 2001. It declares "that the President is authorized to use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons..."

Although ISIS didn't exist on September 11, 2001, and wasn't associated with al-Qaeda, Obama began waging war on the group under the auspices of the 2001 AUMF.

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Few Americans understand the ways that Obama has made it easier for future presidents to wage war. This is due in part to the peculiar way Obama has set these precedents: he has done so while purporting to be a critic of executive power.

It isn't just the aura of being a former constitutional-law professor and civil libertarian. He literally declared, "The President does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation." And he emphatically stated, "History has shown us time and again that military action is most successful when it is authorized and supported by the legislative branch. It is always preferable to have the informed consent of Congress prior to any military action."

(Read More: Obama's Dramatic Reversal on Bush's Laws of War)

As Goldsmith points out, his words are deeply at odds with his actions. Two years remain in his presidency. And unless Obama alters the course he has followed, he will leave office having set precedents that take the brakes off the war machine. Future presidents will be able to wage war without Congress practically anywhere. There is, this week, a glimmer of hope that he'll at least seek legislative approval to keep fighting ISIS. "I will begin engaging Congress over a new authorization for military force," he said.

Is he telling the truth this time? Stay tuned.

Full audio of Goldsmith's remarks is here. Thanks to the Lawfare podcast for airing them and the Hoover Institution for hosting the speech, "President Obama's War-Powers Legacy."