The Justice Department is defending the legality of President Obama's recent recess appointments, releasing Thursday a 23-page legal opinion that critics say is "unconvincing" and whose timing doesn't coincide with the president's decision.

The memo, justifying appointments made last week while Congress was technically not recessed, concludes what the White House claimed at the time -- that Congress isn't able to do business during "pro forma" sessions so it counts as a break.

"The convening of periodic pro forma sessions in which no business is to be conducted does not have the legal effect of interrupting an intrasession recess otherwise long enough to qualify as a 'Recess of the Senate' under the Recess Appointments Clause," reads the Jan. 6 memo written by Assistant Attorney General Virginia Seitz.

"In this context, the president therefore has discretion to conclude that the Senate is unavailable to perform its advise-and-consent function and to exercise his power to make recess appointments,' it continues.

The memo, dated two days after President Obama made his controversial appointment of Richard Cordray to the Consumer Financial Protection Bureau and three others to the National Labor Relations Board, summarizes advice given to the White House before the Jan. 4 appointments, an administration official said.

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"The advice was given orally before" Cordray's appointment, the official said. What was released today "is written advice."

White House spokesman Jay Carney added that the Justice Department's legal opinion "was rendered before the decision was made by the president."

"That's my understanding," Carney said. "The opinion was rendered verbally prior to the date of the opinion itself. The opinion was based on advice provided by OLC and it is very standard for, especially a long and as you see, as lengthy opinion as was put out, for those things to be delivered over a period of time, and the time frame for this is very similar to my understanding the previous occasion."

But Republicans and others are doubtful about both the timing and the content.

"The Justice Department opinion is unconvincing," said Senate Judiciary Committee ranking Republican Charles Grassley of Iowa.

"Its conclusion is at odds with the text of the Constitution and the administration's own previous statements. It fundamentally alters the careful separation of powers between the executive and legislative branches that the framers crafted in the Constitution. It relies on no Supreme Court decision and many conclusions are unsupported in law or the Constitution. It recognizes that the courts might well disagree. And it flies in the face of more than 90 years of historical practice," Grassley said in a statement.

"Taken together with a laundry list of other assertions of the power to act without Congress, this is clearly an escalation in a pattern of contempt for the elected representatives of the American people," he continued.

The American Center for Law and Justice, a conservative group focused on constitutional law, also called Thursday's memo a "smokescreen."

"This memo changes nothing: President Obama acted in a unconstitutional manner in making these appointments -- ignoring the rule of law and nearly a century of precedent," said ACLJ Chief Counsel Jay Sekulow.

According to the terms of a recess appointment at the time Obama made it, Cordray, who was successfully filibustered by Republicans last year, will remain in the job until Jan. 3, 2014. He is not personally objectionable to many Republicans, however, they want to change aspects of the agency he was named to lead and which was approved on a party-line vote in the 2010 banking reform bill.

But Republicans angry at Obama's move -- and their allies willing to file suit -- may not have a legal case. Nowhere in the Constitution is a recess expressly defined even though the document gives the chief executive the "power to fill up vacancies that may happen during the recess of the Senate."

As a result, a loose understanding has arisen over the years as to what constitutes a recess.