President Bush and Iraqi Prime Minister Nouri al-Maliki are poised to conclude a bilateral "memorandum of understanding" that would authorize U.S. troops to continue military operations in Iraq. There is only one problem — the memo won't be binding U.S. law.

A memo isn't a "treaty," which requires a two-thirds vote in the Senate under Article 2 of the Constitution. It isn't a "congressional-executive agreement," which requires the approval of a majority of both houses of Congress under Article 1. It is just a statement of intent. According to the State Department's Office of the Legal Advisor, "memo" is the term that is "common for nonbinding documents."

The United States is moving into legal no-man's land because the president refuses to ask the U.N. Security Council to renew the annual resolution that provides the legal foundation for the presence of our troops in Iraq. If this resolution is allowed to expire Dec. 31, it would create a legal vacuum — a vacuum that can't be filled by a presidential memo.

The U.S. needs a solid legal basis for its continuing actions in Iraq to replace the U.N. mandate. There must be a new agreement on day-to-day issues such as the resupply of goods to the troops, which are usually exclusively resolved by the president in his capacity as commander in chief. But more important, this deal also covers questions at the center of far-reaching policy debates that rightly require congressional participation — the timetable for the withdrawal of U.S. troops central among them.

In the attempt to reach an accord with al-Maliki, the president made news by negotiating a "general time horizon" for withdrawing troops — but he hasn't been willing to take the agreement to Congress and deal with Democrats in order to create a sound constitutional foundation for an enduring and bipartisan policy.

Once the deal is signed by both parties, it's quite possible that the president will proclaim that this memo is special and can serve as a legal basis for all our activities in Iraq. If he does, he will be acting unconstitutionally. No precedents support the presidential creation of legally binding commitments on the use of force without congressional consent.

Resorting to the use of a memo also undermines democracy in Iraq, the very democracy we went to war to create. Just as it allows Bush to avoid Congress, it allows al-Maliki to make an end run around his own parliament, which, according to the Iraqi Constitution, must approve formal international agreements; al-Maliki is widely expected to sign the memo unilaterally.

That will only make it easier for the next Iraqi prime minister to repudiate the entire deal on grounds that the memo was made unconstitutionally.

Despite the president's claim that he is creating a solid basis for future cooperation, his initiative will leave the fate of the American military at the mercy of Iraqi politics.

At the same time, the expiration of the U.N. resolution, without a clearly legitimate alternative in place, could invite U.S. lawsuits challenging the ongoing use of force in Iraq. The courts might try to avoid deciding the merits of these cases, but the litigation would further polarize U.S. politics and leave the military uncertain about the legitimate range of its activities in a war zone.

A simple solution protects the troops and does not require us to forfeit our most basic constitutional values: Extend the U.N. mandate for six months and allow the next president to negotiate an agreement that can gain the support of Congress and the American people.

It is past time for a lame-duck president to recognize that the country has paid a sufficient price for his extravagant unilateralism.

Bruce Ackerman and Oona Hathaway are professors of law at Yale and the University of California, Berkeley, respectively. They wrote this commentary for the Los Angeles Times.