The answer is one that perhaps only a lawyer could love: There is a long tradition that the Justice Department defends laws adopted by Congress and signed by a president, regardless of whether the president in office likes them.

This practice cuts across party lines. And it has caused serious heartburn for more than one attorney general.

The tradition flows directly from the president’s constitutional duty to take care that the laws are faithfully executed, says Paul Clement, who served four years in President George W. Bush’s administration as solicitor general, the executive branch’s top lawyer at the Supreme Court.

Otherwise, Clement says, the nation would be subjected to “the spectacle of the executive branch defending only laws it likes, with Congress intervening to defend others.”

That is why solicitors general not only serve the president who nominated them but also have a special duty to Congress, “most notably, the vigorous defense of the statutes of this country against constitutional attack,” Justice Elena Kagan testified to Congress in 2009 after Obama nominated her to be solicitor general. She joined the Supreme Court a year later.

On occasion, the Justice Department will even defend a law it knows is likely to be judged unconstitutional, said Seth Waxman, who served as President Bill Clinton’s solicitor general.

Six federal judges had ruled against the Communications Decency Act, a 1996 law that made it a crime to make available to minors on the Internet material that was “indecent” or “patently offensive.” Nevertheless, Waxman backed the law in an appeal to the Supreme Court. He lost there, but felt good about serving “our adversarial system of constitutional adjudication.”

William French Smith, President Ronald Reagan’s first attorney general, once said that defending congressional action that extended the ratification period for the proposed Equal Rights Amendment for women caused far and away his most uncomfortable moments in four years in office because of the irate calls he got from administration supporters — who staunchly opposed the ERA.

Obama’s supporters have similarly criticized the administration for its legal efforts on behalf of “don’t ask, don’t tell,” the law that bars gays from serving openly in the military, even after U.S. District Judge Virginia Phillips in Riverside, Calif., ordered the military to immediately suspend and discontinue any investigation or other proceeding to dismiss gay service members under the law.

Indeed, Justice lawyers delayed their response to Phillips because the White House weighed in on the matter, according to a government official with knowledge of the situation. A couple of White House lawyers did not want to seek a court order that would temporarily suspend the judge’s ruling, this person said, speaking on condition of anonymity to discuss the administration’s internal deliberations. Failing to challenge the ruling would have had the effect of ending the policy.

Obama says he supports repeal of “don’t ask, don’t tell” but only after careful review and an act of Congress.

Ultimately, the government did ask Phillips to suspend her ruling pending the government’s appeal.

After Phillips refused, the administration asked the federal appeals court in San Francisco to freeze her ruling temporarily, which it did late Wednesday. Justice lawyers argued that while appeals were pending, abruptly ending “don’t ask, don’t tell” and immediately allowing openly gay service members could harm troop morale and unit cohesion when the military is fighting two wars.

On rare occasions, Justice officials conclude there is no reasonable argument that can be made in defense of a federal law.

Clement recalled two instances during his tenure. One posed free speech problems, because it sought to prevent recipients of federal transportation money from running ads favoring legalization of some drugs. The other was an obscure 1800s statute dealing with licensing of salvage operations.

When George H.W. Bush was president, he vetoed the Cable Television Act of 1992 in the belief that certain provisions were unconstitutional. The bill became law when Congress overrode Bush’s veto.

Cable operators challenged the law in court, and Bush’s Justice Department said it would not defend what the president had vetoed.

But then Clinton was elected. He reversed course and sent Justice lawyers into court on behalf of the law. The Supreme Court eventually upheld it.