The phrase "a constitutional obligation" is correct and usable in written English.
It can be used when referring to a duty or responsibility that is mandated by a constitution.
Example: "The government has a constitutional obligation to protect the rights of its citizens."
Alternatives: "a legal duty" or "a constitutional requirement".
"There was a constitutional obligation to legislate this offense, but it was not against the constitution to create an offense that was of no use," he said.
Politicians have a constitutional obligation to protect public education.
Providing poor defendants effective appointed counsel is more than a constitutional obligation.
But competent counsel is also a constitutional obligation of a defense lawyer.
The I.M.F. has a constitutional obligation to avoid making loans in which wishful thinking informs the repayment schedule.
"I believe personally we have a constitutional obligation, responsibility to do congressionally directed spending," Mr. Reid said.
"We have a constitutional duty and ethical obligation to make sure we don't do a shitty job for our clients," said Michael Nachmanoff, the federal public defender in the Eastern District of Virginia.
The Senate has a constitutional responsibility and an institutional obligation in this effort.
"Conducting the census is a vital constitutional obligation," Representative John A. Boehner of Ohio, the House minority leader, said Thursday.
Nobody knows how to reconcile them not only with higher spending on education but also with a new constitutional obligation to cut the federal government's budget deficit almost to zero by 2016.
The decision rested, he wrote, on "the theory that two governments accord more liberty than one," which he said gave rise to a "grave constitutional obligation if democratic liberty and the federalism that secures it are to endure".
