WASHINGTON — The powers of an American president to wage war have grown stronger for nearly two decades, ever since the Sept. 11 attacks led the United States into an era of perpetual conflict.
Those powers are now in the hands of the most volatile president in recent memory.
President Trump’s decision to authorize the killing of a top Iranian military leader could be the match that sets off a regional conflagration, or it could have only marginal geopolitical impact like so many of the targeted killings ordered by Mr. Trump and his predecessors. But it is just the latest example of the capricious way in which the president, as commander in chief, has chosen to flex his lethal powers.
From his dealings with Iran, Syria, Yemen and Afghanistan, Mr. Trump has shown little evidence over the past three years that his decisions about war and peace are made after careful deliberation or serious consideration of the consequences.
In June, Mr. Trump shocked his vice president, his national security adviser and his secretary of state when he reversed himself and called off a strike against Iran with only 10 minutes to spare. That decision, days after Iran downed an American reconnaissance drone, came in part after Mr. Trump consulted Tucker Carlson, the Fox News personality, who reminded the president that he had pledged to get out of foreign conflicts rather than begin new ones. A strike on Iran, Mr. Carlson said, could anger the president’s political base.
A little more than six months later, Mr. Trump ordered the killing of Maj. Gen. Qassim Suleimani, who led Iran’s powerful Quds Force of the Islamic Revolutionary Guards Corps. It was a move — set in motion after a rocket attack on Dec. 27 by forces linked to Iran killed an American contractor in Iraq — that Presidents George W. Bush and Barack Obama considered too provocative to authorize.
The war-making powers that Congress granted to the president in the years since the Sept. 11 attacks, combined with stunning advances in the technology of man-hunting, have given the inhabitant of the Oval Office the power to track and kill individuals practically anywhere on earth. General Suleimani was not even a particularly difficult target at Baghdad International Airport on Friday, when his convoy was hit by missiles fired by an American MQ-9 Reaper drone.
There have been attempts by lawmakers in recent years to limit the president’s abilities to wage new or expanded wars based on the authorities Congress granted in the years after the Sept. 11 attacks. But with little support from leaders of both parties on Capitol Hill, those efforts have generally gone nowhere.
“Our country has, quite self-consciously, given one person, the President, an enormous sprawling military and enormous discretion to use it in ways that can easily lead to a massive war. That is our system: one person decides,” Jack Goldsmith, a Harvard Law professor and former Justice Department official during the George W. Bush administration, wrote on Friday on Twitter.
Mr. Trump’s suspicions about the national security and intelligence bureaucracy he inherited have guided his unorthodox decisions on other aspects of foreign policy, like writing flattering, personal letters to the leader of North Korea, Kim Jong-un, and outsourcing much of his policy toward Ukraine to Rudolph W. Giuliani, his personal lawyer. There has been a dizzying turnover in his national security team: In three years, the president has had four national security advisers, two secretaries of state, two defense secretaries and one acting defense secretary.
How Mr. Trump sees the killing of General Suleimani as advancing his broader agenda on Iran is unclear, and on Friday he seemed to portray the operation as something of a one-off: a necessary step to ensure that tensions between the United States and Iran do not spiral out of control. General Suleimani was plotting “imminent and sinister attacks” before “we caught him in the act and terminated him,” the president said from his resort in Palm Beach, Fla., although administration officials did not describe any threats that were different from what they said the general had been orchestrating for years.
“We took action last night to stop a war. We did not take action to start a war,” Mr. Trump said. The president’s decision to kill the general at this time appeared to many military experts as a potentially reckless escalation. But his policy toward Iran, what administration officials call a “maximum pressure” campaign, has long underestimated how the country would respond to economic sanctions that have crippled its economy.
When Iranian operatives blew holes in oil tankers in the Gulf of Oman in June and launched drone strikes on Saudi oil facilities in September, Mr. Trump opted in both cases against a direct, immediate military response. Still, one day after the drone strike targeting General Suleimani, the Pentagon announced it was sending around 3,000 more troops to Kuwait as a precaution against growing threats to American forces in the region.
Lindsay P. Cohn, a professor of political science at the Naval War College, said that Mr. Trump appears to be convinced that General Suleimani’s death will not lead to a significant surge of violence in the Middle East. It satisfies two imperatives for him: appearing to look tough without taking on, at least for now, any new commitments.
“He doesn’t want to get entangled. But he doesn’t want to look weak,” said Professor Cohn, adding that her opinions did not necessarily represent those of the Defense Department.
The president’s mercurial approach to Iran has left a trail of alienated allies — including European NATO allies angry about his decision to withdraw from the 2015 Iran nuclear deal and Arab nations in the Persian Gulf region uncertain about Mr. Trump’s resolve to support them in the face of direct attack from Iran.
Mr. Trump’s blunt language about the folly of the wars in Iraq and Afghanistan led some to conclude that he was shy about using force. The evidence shows the opposite, said Micah Zenko, a national security expert who writes frequently about American presidents and the use of military power.
During the three years of the Trump administration, airstrikes in Afghanistan, Iraq and Somalia have sharply increased, as have civilian casualties, Mr. Zenko said. But rather than centralizing decisions about lethal force inside the White House, Mr. Trump has often devolved authority to military commanders.
Mr. Zenko described the president as a “passive hawk,” wanting to appear tough without making decisions about military force that could incite long-term commitments.
Less than 10 days in office, Mr. Trump authorized a risky commando raid in Yemen that killed several civilians and one Navy SEAL, Chief Petty Officer William Ryan Owens. Amid criticism for the botched raid, Mr. Trump put the blame on military commanders who, he said, “lost Ryan.”
Twice Mr. Trump ordered cruise missile attacks against the government of President Bashar al-Assad in Syria in retaliation for chemical attacks on civilians there, something that Mr. Obama decided against. Administration officials said that Mr. Trump was particularly impressed by the success of the Special Operations raid in October that killed Abu Bakr al-Baghdadi, the leader of the Islamic State, something that may have led the president toward approving the killing of General Soleimani.
One of Mr. Trump’s former national security advisers, John R. Bolton, who was pushed out in September because the president considered him an irritant and too much of a hawk, was suddenly praising Mr. Trump on Friday.
The killing of General Suleimani was the type of strike that Mr. Bolton had long advocated — and Mr. Trump had once rebuffed — and the former aide tweeted that he hoped it would be the “first step toward regime change in Iran.”