WASHINGTON – A retired Air Force general urged the Senate on Tuesday to proceed with caution when looking for ways to limit the president’s authority to launch a nuclear attack.

“Conflicting signals can result in loss of confidence, confusion or paralysis in the operating forces at a critical moment,” said Robert Kehler, former commander of the United States Strategic Command.

Two other witnesses also warned Sen. Bob Corker, who called the hearing, and other lawmakers that any attempts to restrict the president’s power to order nuclear strikes could have unintended consequences.

“I’m not sure that’s a wise choice,” said Brian McKeon, a former top policy official in the Defense Department.

“I would be very wary of legislative fixes,” added Peter Feaver, a Duke University professor of political science and public policy.

Concerns that a president could order a preemptive nuclear strike are on the rise in Congress as President Donald Trump continues to trade insults with North Korean dictator Kim Jong Un.

For the first time in more than four decades, the president’s powers to call up the nation’s nuclear arsenal were the subject of a congressional hearing on Tuesday.

“Making the decision to go to war of any sort is a heavy responsibility for our nation’s elected leaders, and the decision to use nuclear weapons is the most consequential of all,” said Corker, chairman of the Senate Foreign Relations Committee, which held the hearing.

Corker said the time has come to examine “the realities” of the president’s authority to order a nuclear attack. But the Tennessee Republican, who warned last month that Trump’s rhetoric could be setting the nation on a path to World War III, insisted the hearing should not be seen as an attempt to specifically rein in Trump.

“This shouldn’t be taken as something that is specific to anyone,” he said.

Democrats on the committee left no doubt that Trump was their target.

“We are concerned that the president of the United States is so unstable, is so volatile, has a decision-making process that is so quixotic that he might order a nuclear weapons strike that is wildly out of step with U.S. national security interests,” said Sen. Chris Murphy, D-Conn.

Many Americans fear that Trump’s bombastic words could turn into “nuclear reality,” said Sen. Ed Markey, D-Mass.

“Under existing laws, the president of the United States can start a nuclear war – without provocation, without consultation and without warning,” he said. “It boggles the mind.”

As commander-in-chief, the president has the sole authority to order a nuclear a strike. While existing procedures call for the president to consult first with military and civilian leaders, the final decision rests with him.

Markey and Rep. Ted Lieu, D-Calif., have each filed bills that would prohibit the president from launching a preemptive nuclear strike without a declaration of war by Congress.

McKeon and others questioned the wisdom of such legislation. McKeon suggested Congress’ constitutional power to declare war already gives it the authority to stop the president from ordering a preemptive first strike.

Kehler suggested top military leaders also could act as an important check against the president. While the president has the final word on ordering a nuclear strike, the military would be responsible for carrying out such an order.

Military leaders could refuse to follow any order that they deemed illegal or that had not been vetted through the proper channels, Kehler said.

“The military does not blindly follow orders,” Kehler said. “That is true of nuclear orders as well.”

Instead of looking to curtail the president’s nuclear powers, Feaver suggested Congress should consider upgrading nuclear command and control technology, which he said has been neglected and has become outdated.

Corker said after the hearing that he expects Congress to continue to review questions about the president’s authority “because it is a sobering issue.

“I do not see a legislative solution today,” he said. “But that doesn’t mean that over the course of next several months one might develop.”

Markey said he remained concerned about the president’s powers to start a nuclear war.

“I don’t think the assurances I’ve received today will be satisfying to the American people,” he said. “I think they can still realize that Donald Trump can launch nuclear codes just as easily as he can use his Twitter account, without the checks and balances of the United States Congress.

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An influential Republican who warned just a month ago that President Trump could be leading the nation on the path to World War III said Tuesday the time has come for Congress to review “the realities” of the president’s authority to order a nuclear attack.

“To be clear, I would not support changes that could reduce our deterrence of adversaries or reassurance of allies,” Sen. Bob Corker, chairman of the Senate Foreign Relations Committee, said at the opening of a Senate hearing on the president’s powers to launch a nuclear strike.

But the Tennessee Republican noted that it has been more than 40 years since a congressional committee has reviewed the president’s unchecked powers over the nation’s nuclear arsenal.

“Making the decision to go to war of any sort is a heavy responsibility for our nation’s elected leaders,” Corker said. “And the decision to use nuclear weapons is the most consequential of all.”

Congress needs to explore “the realities of this system,” he said.

Asked before the hearing if he was worried about Trump having access to the nation’s nuclear arsenal, Corker said, “This (hearing) is not specific to anybody.”

Tuesday’s hearing comes as Trump continues to trade insults with North Korean dictator Kim Jong Un and amid concerns by some members of Congress about the executive branch’s authority to wage war, particularly with nuclear weapons.

“The committee is clearly looking for remedies to ensure that a demented president could not unilaterally start a nuclear conflagration,” said Bruce Blair, an expert on nuclear command and control and a research scholar at the Program of Science and Global Security at Princeton University.

As commander-in-chief, the president has the sole authority to order a nuclear a strike. While existing procedures call for the president to consult first with military and civilian leaders, the final decision rests with him.

“No one can veto the president’s decision,” Blair said.

Some members of Congress are pushing for a check on the president’s powers, particularly his ability to order a preemptive strike.

Bills filed in January by Rep. Ted Lieu, D-Calif., and Sen. Ed Markey, D-Mass., would prohibit the president from launching a preemptive nuclear strike without a declaration of war by Congress. Neither piece of legislation has gained any traction in the Republican-controlled Congress.

But Trump’s aggressive approach toward North Korea continues to raise fears that his rhetoric might backfire and further inflame tensions. Trump threatened in August to unleash “fire and fury like the world has never seen” in response to reports that the communist regime had developed a warhead that could be mounted on a ballistic missile.

In an interview with The New York Times, Corker, Trump’s most outspoken Republican critic in Congress, accused Trump of undermining diplomacy efforts by Secretary of State Rex Tillerson and warned that the president’s actions could set the nation on the path to World War III.

At Tuesday’s hearing, senators will hear from C. Robert Kehler, a retired Air Force general who served as commander of the United States Strategic Command; Peter D. Feaver, a political science and public policy professor at Duke University; and Brian McKeon, former acting under secretary for policy at the Defense Department.

The hearing is one in a series the committee is holding on war making and foreign policy. Last month, the panel examined whether it’s time to update the resolution authorizing the president to order the use of military force in foreign countries.

Corker said afterward that he expects the committee to take up a new military-force authorization resolution “fairly soon.”