By Marisa Taylor and Jonathan S. Landay, McClatchy Washington Bureau (TNS)

WASHINGTON — As U.S. military operations against the Islamic State approach the one-year mark, the White House has failed to give Congress and the public a comprehensive written analysis setting out the legal powers that President Barack Obama is using to put U.S. personnel in harm’s way in Iraq and Syria.

The absence of an in-depth legal rationale takes on greater urgency with Obama’s decision this week to dispatch up to an additional 450 U.S. military trainers and other personnel to Iraq and to establish a second training site for Iraqi forces in war-ravaged Anbar province, most of which is under Islamic State control.

The only document the White House has provided to a few key lawmakers comprises four pages of what are essentially talking points, described by those who’ve read them as shallow and based on disputed assertions of presidential authority.

“It’s very thin,” Rep. Adam Schiff of California, the senior Democrat on the House Intelligence Committee, said of the document.

Schiff contended that without a new congressional resolution that specifically confirms the president’s power to intervene militarily against the Islamic State in Iraq and Syria, Obama is overseeing a dangerous expansion of presidential war-making powers.

“This is opening the door to future presidents making war without any reliance on congressional authorization,” said Schiff. He added that Congress also is to blame because it has failed to pass a new resolution expressly authorizing the deployment of U.S. military trainers, advisers and security units to Iraq and the use of U.S.-led airstrikes that have been staged against the Islamic State in Iraq since August and in Syria since September.

The absence of a public legal analysis — replete with court rulings and historical precedents — constrains public debate on the growing U.S. military role in the tumultuous Middle East nearly four years after Obama pulled U.S. combat troops out of Iraq, and has hampered congressional efforts to forge a new resolution on the Islamic State, also known as ISIL or ISIS.

“The burden is on the administration to come forward and ensure that its legal basis is justified and appropriate,” said Raha Wala, senior counsel for Human Rights First, a nonprofit New York-based advocacy group. “In any democracy, we can’t operate with secret law.”

More significantly, by not setting out a legal case in public documents, Obama may be trying to preserve his flexibility to authorize new operations against the Islamic State or other extremist groups elsewhere, unfettered by constraints that could be imposed by Congress.

In his secretive and expansive view of presidential powers, some experts see Obama following the lead of his predecessor, George W. Bush.

The administration’s only public articulation of its legal position has come in speeches, letters and the four-page document provided to key lawmakers — titled “Legal Basis for U.S. Military Operations in Syria” — that was drafted around the same time of the first U.S. airstrikes on the Islamic State in Syria. By contrast, a secret 2010 Justice Department opinion — released by the administration under court order — that authorized the targeted killing of American leaders of al-Qaida runs 31 pages and cites extensive examples of domestic and international laws and U.S. court decisions in setting down a comprehensive framework for such operations.

When it comes to Syria and Iraq, the administration “has clearly articulated our legal authorities in numerous public venues including White House press briefings, congressional testimonies and other forums,” said a White House official who is knowledgeable of the issue but wasn’t authorized to speak publicly as a matter of practice.

The president’s legal team “engaged with lawyers from key departments and agencies in discussions about the underlying authorities for those actions,” said the White House official.

“It defies common sense to believe that the president has taken this type of action based on a four-page set of bullet points and not a full legal analysis by either the Office of Legal Counsel or the White House counsel,” said Chris Anders, senior legislative counsel for the American Civil Liberties Union. “This is too important of a decision to be made without that kind of legal advice.”

Initially, the administration argued that Obama could authorize military operations under Article Two of the Constitution, which designates him as the commander in chief of the U.S. armed forces.

But under fire from Congress, the administration adopted as its main arguments for Obama’s authority the 2001 congressional resolution that authorized the use of force against al-Qaida and “associated forces” and the 2002 resolution approving the invasion of Iraq and the overthrow of the late dictator Saddam Hussein.

The 2001 resolution “authorized the use of force against ISIL beginning in at least 2004, when ISIL, then known as al-Qaida in Iraq, pledged its allegiance to (the late Osama) bin Laden,” says the four-page document. “The recent split between ISIL and al-Qaida’s current leadership does not remove ISIL from coverage.

“Although the threat posed by Saddam Hussein’s regime in Iraq is the focus of the 2002 (resolution), the statute … has always been understood to authorize the use of force for additional purposes,” it says.

Those administration assertions, however, only generated more heat.

Critics dismissed the White House’s assertion that the Islamic State is an appendage of al-Qaida, pointing to the 2014 rupture between the two extremist organizations and the ongoing battles they’re fighting in Syria. Moreover, they say, the Islamic State didn’t exist in 2001.

Critics also reject the administration’s reliance on the 2002 resolution because Saddam is no longer in power and the situation in Iraq is radically different.

“There’s no question in my mind that the ongoing war against ISIL goes well beyond the existing 2001 and 2002 (resolutions),” said Sen. Tim Kaine, D-Va., who this week introduced with Sen. Jeff Flake, R-Ariz., draft legislation that would authorize the U.S. campaign against the Islamic State.

The White House and the Justice Department have refused to even acknowledge if the president has sought a written legal analysis underpinning his authority. The White House referred McClatchy to the Justice Department, which declined to comment.

(Anita Kumar contributed to this report.)

(c)2015 McClatchy Washington Bureau. Distributed by Tribune Content Agency, LLC.

File photo: U.S. President Barack Obama speaks on the legislation he sent to Congress today to authorize the use of military force (AUMF) against Islamic State in the Roosevelt Room of the White House Feb. 11, 2015 in Washington, D.C. (Olivier Douliery/Abaca Press/TNS)