WASHINGTON — President Trump has become the third president to renew a post-9/11 emergency proclamation, stretching what was supposed to be a temporary state of national emergency after the 2001 terror attacks into its 17th year.

But the ongoing effects of that perpetual emergency aren't immediately clear, because the executive branch has ignored a law requiring it to report to Congress every six months on how much the president has spent under those extraordinary powers, USA TODAY has found.

Exactly 16 years ago Thursday, President Bush signed Proclamation 7463, giving himself sweeping powers to mobilize the military in the days following terrorist attacks that crashed planes into the World Trade Center, the Pentagon, and a Pennsylvania field. It allowed him to call up National Guard and Reserve troops, hire and fire military officers, and bypass limits on the numbers of generals that could serve.

Presidents Bush and Obama renewed that emergency each year. And on Wednesday, Trump published a now-routine notice in the Federal Register extending the emergency for the 16th time, explaining simply that "the terrorist threat continues."

But as Trump extends the emergency into a third presidential administration, legal experts say a review of those powers is long overdue.

"The president is given these emergency powers as a temporary measure until Congress has time to act. It stretches credulity to think Congress hasn’t had time to act since 9/11 happened," said Elizabeth Goitein, co-director of the Liberty and National Security Program at the Brennan Center for Justice. "We should not be treating 9/11 as an emergency in 2017."

The perpetual war footing has had a striking lack of examination. Under the National Emergencies Act — a post-Watergate law intended to rein in presidential emergency powers — the president needs to renew the emergency each year or it lapses. But Congress is also supposed to review each emergency every six months. It never has.

And it's not just 9/11. Presidents have declared scores of emergencies over the past 40 years, dealing with everything from the Iran Hostage Crisis to the Swine Flu. More than 30 of those national emergencies remain in effect — and Congress has never reviewed a single one in the history of the National Emergencies Act.

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In his first eight months in office, Trump has kept in place the states of emergency put in place by his predecessors. But he's also signaled that he may make novel use of emergency powers. He said last month that he was drawing up papers to declare a state of national emergency to address opioid addiction, a unique public health crisis unlike the infectious diseases that have prompted previous emergencies.

Also last month, Trump set aside congressionally mandated pay increases for military and civilian employees, cutting them to 2.1% for uniformed services and an average of 1.9% for civilians. The law allows the president to cut scheduled pay raises in cases of "national emergency or serious economic conditions affecting the general welfare."

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The law also requires the president to report to Congress every six months about the cost of each national emergency. And on the 9/11 proclamation, it appears that no president — not Bush, nor Obama, nor Trump — has even done that.

In a 2003 executive order, President Bush delegated the reporting task to the Secretary of Defense.

USA TODAY requested copies of those reports dating back to 2001 under the Freedom of Information Act. After searching its records for more than two years, the Defense Department responded that "no records of the kind you described could be identified." And according to the Congressional Record, no reports have ever been received.

A Pentagon spokesman could not immediately explain why the Secretary of Defense has never submitted the required reports to Congress.

Congress's continued neglect of its oversight of national emergencies comes as it debates a related question of the war powers given to the president after the 2001 terrorist attacks. On Wednesday, the Senate scuttled a proposed amendment by Sen. Rand Paul, R-Ky. that would have revoked the open-ended authorizations for the use of military force enacted by Congress in 2001 and 2002, with the hope of prompting debate on a more limited authorization.

At the same time, the Pentagon has stopped releasing regular reports on the number of National Guard and Reserves called up to serve overseas as a result of the 2001 emergency. The most recent figures from 2015 show about 18,000 guard and reserve troops remained involuntarily activated — mostly under that 2001 state of emergency.

"We used to call this 'the new normal.' Now it's just normal," said John Goheen of the National Guard Association of the United States. "Guard leaders, what they’re most worried about is what would happen if the Army and Air Force stopped using us. They want to serve."

But he said it's important to constantly re-examine the role of guard and reserve troops in the global war on terror. "This is an interesting debate, and it deserves more attention," he said.