WASHINGTON -- President George W. Bush spoke with his military commander in Iraq nearly every week.

President Barack Obama was so deeply involved in military operations that his first three Defense secretaries all complained, sometimes bitterly, about what they considered White House micromanagement.

In nearly five months in office, President Donald Trump has yet to meet or speak with either his Iraq or Afghanistan commander, even as his administration weighs deeper and longer-term involvement in both conflicts and asks Congress for a vast increase in defense spending.

Trump's hands-off approach to America's longest wars demonstrates how much control his administration has entrusted to Defense Secretary James N. Mattis, a retired four-star Marine general, and commanders on the ground.

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Senior Pentagon officials and military officers who often chafed under Obama's centralized decision-making have welcomed the shift, saying it has freed them to carry out operations based on military, and not political, considerations.

But it also raises concerns that Trump has given too much latitude to the Pentagon, which already has been accused of more indiscriminate bombings than in the past, causing an increase in civilian casualties.

"The idea of the 10,000-mile screwdriver from Washington making decisions for a field commander, as has been the case over the past decade, is flawed," said James Stavridis, a retired admiral who served as NATO supreme commander and is now dean of the Fletcher School of Law and Diplomacy at Tufts University.

"We need to be cautious that we do not go so far in the other direction that we end up with rogue commanders," Stavridis added. "The White House needs to lay out a strategic vision but then let commanders do the tactical execution."

The president already has granted Mattis authority to raise troop levels in the wars in Iraq and Syria, a power usually held closely by the White House.

Trump is expected to grant Mattis the same authority in Afghanistan, where civilian casualties have soared in fighting this year. The Taliban now controls or contests more than 40 percent of Afghan territory -- holding more ground than at any point since the U.S.-led invasion in 2001, according to recent United Nations estimates.

The president also has authorized his commanders to move more aggressively against militants in Somalia and Yemen, where U.S. special operations forces have stepped up raids against Islamic State and other terrorist groups.

"What I do is I authorize my military," Trump said on April 13 after the Air Force dropped the most powerful conventional bomb in its arsenal on an Islamic State complex in eastern Afghanistan, a decision that was made without White House input.

"We have the greatest military in the world, and they've done the job, as usual," Trump said. "We have given them total authorization, and that's what they're doing."

A White House official, who wasn't authorized to speak on conversations in the chain of command, said the delegation of authority has enabled commanders to take a "more aggressive approach" in which missions are executed with "more speed and more efficiency."

"That is in no small part due to the fact that the president is putting his trust in the generals, not tying their hands and micromanaging their ability to fight the fight they need to fight," the official said.

Trump has regular working dinners with his national security team in his personal dining room at the White House, aides say, and thus remains briefed on major operations.

His companions include Mattis, Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff; Lt. Gen. H.R. McMaster, Trump's national security advisor; and Homeland Security Secretary John F. Kelly, another retired four-star Marine general.

"They have great rapport with one another," the White House official said. Mattis and Dunford usually dine with Trump once a week, sometimes in a group, sometimes one-on-one, the official said.

"The president does respect the chain of command and he gets the vast majority of his information from the top echelons of his national security teams," the official said.

The generals running the wars -- Lt. Gen. Stephen Townsend in Iraq and Gen. John W. Nicholson Jr. in Afghanistan -- are "three or four echelons below" the president, the official said.

Both commanders recently completed sweeping written assessment of the conflicts they oversee. Still, the official said, the president is "keeping with the chain of command" by not communicating with them directly.

It hasn't taken long for ground commanders to exercise their newfound freedom under Trump -- and for it to backfire.

In April, Adm. Harry B. Harris Jr., the Pentagon's top commander in the Pacific, announced that he had ordered the aircraft carrier Carl Vinson and its escort ships to detour north from Singapore to North Korea amid rising tensions with the nuclear-armed regime.

Trump quickly boasted that an "armada" was racing toward the Korean peninsula, suggesting a confrontation was possible.

The Pentagon was left scrambling a week later, and the White House was caught flat-footed, when it emerged that the Carl Vinson had instead sailed south to conduct exercises in the Indian Ocean, 3,500 miles away from the Korean peninsula. Harris later apologized to Congress for the confusion.

Nicholson, the U.S. commander in Afghanistan, similarly surprised the White House when he authorized use of the so-called mother of all bombs against an Islamic State tunnel complex.

Officials said later that Nicholson did not foresee how the giant bomb, which had never been used in combat before, would generate headlines around the globe and be interpreted as a sign that Trump would be more aggressive than previous presidents.

Both Harris and Nicholson had the authority to make those decisions under Obama. But it's unlikely either would have taken such action without first seeking approval from the White House, according to officials.

In one incident last year, the Pentagon waited for White House approval to move three Apache attack helicopters from Iraq to Syria in the fast-moving fight against the Islamic State. Obama finally approved the transfer shortly before he left office.

Obama's first three secretaries of Defense-- Robert M. Gates, Leon E. Panetta and Chuck Hagel -- all accused the administration of needlessly interfering in military matters, though they did so after leaving office.

"The controlling nature of the Obama White House and the staff took micromanagement and operational meddling to a new level," Gates wrote in his 2014 book, "Duty."

Ned Price, the National Security Council spokesman under Obama, argued that careful deliberations often resulted in better policy decisions.

"What our critics would label 'micromanaging' was the Obama White House taking prudent steps to ensure that the decisions of one component complemented the broader U.S. government approach," he said. "Indeed, failing to do so can be a detriment to our strategic goals for the country or region in question and ... place our men and women in uniform at greater risk."

The risk of Trump's hands-off policy, at least for the Pentagon, was clear when he seemed to accept no responsibility after a U.S. military raid in Yemen that he had personally authorized went awry nine days after he took office.

He instead appeared to blame "the generals" for the death of Navy SEAL Chief Petty Officer William "Ryan" Owens in the ill-fated Jan. 29 raid, which also killed more than a dozen civilians, including women and children.

"They came to me, they explained what they wanted to do _ the generals _ who are very respected, my generals are the most respected that we've had in many decades, I believe," Trump told Fox News. "And they lost Ryan."

Anthony Cordesman, a former intelligence director at the Pentagon now with the Center for Strategic and International Studies, a Washington think tank, said the military will carry out tactics to execute a president's policy but cannot develop its own policy.

"Military operations should not be micromanaged but they cannot go unmanaged either," he said. "A president has to take responsibility for his own policy and overarching strategic goals. That is not something that can be delegated."