President Donald Trump’s role in inciting the shocking events at the Capitol on Jan. 6 and concerns about his state of mind highlight the grave risks posed by the policy that gives presidents the sole authority to order the use of nuclear weapons — without the need for consultation or agreement by anyone. This danger is heightened by a second policy that allows the United States to use nuclear weapons — not just in response to a nuclear attack, but also first during hostilities.

While this arrangement appears especially risky now, giving any one person the authority to order the use of nuclear weapons is inherently risky and completely unnecessary. Any use of nuclear weapons would be devastating and should require both a presidential order and the agreement of two other officials.

Unlike decades ago, when sole authority was first established, there is a straightforward way to include other officials in a launch decision. President-elect Joe Biden should make this long-overdue change once in office by limiting his own authority to order a nuclear attack.

The government continuously tracks the location of officials in the presidential line of succession and maintains the ability to quickly and securely communicate with them so that if the president dies or is incapacitated, presidential authority seamlessly devolves to the next person in line. This capability, implemented by the Federal Emergency Management Agency, allows the Pentagon’s war room — which would issue the launch order to bomber and missile crews — to be confident that any order is coming from the current president.

The FEMA system would also allow the war room to quickly and securely communicate with these additional officials to get their assent to or veto of the launch order.

There are compelling reasons to designate the next two people in the presidential line of succession for this important role. Normally these would be the vice president and the speaker of the House. (The next four are the president pro tempore of the Senate, the secretary of state, the secretary of treasury and the secretary of defense.)

These people have the political legitimacy to take part in a decision to use nuclear weapons since they would become the commander in chief and assume the authority to order a nuclear attack if the officials above them were no longer in power.

These people would also provide some degree of democratic input: The top three officials in the line are elected, and two are members of Congress. Unless several top officials died or were incapacitated, at least one congressional leader would need to agree with an order to use nuclear weapons. Moreover, these officials cannot be fired and replaced by the president, as Cabinet secretaries could.

Current concerns about Mr. Trump’s state of mind make clear that it is essential to place checks on a president’s ability to order a nuclear launch. Before carrying out a launch order, the Pentagon must determine that it is “valid” — that it comes from the current president and that the president is mentally fit to issue the order. These other two officials would be in a good position to judge the president’s state of mind, and either could veto the order if they thought the president was unstable, as well as if they thought the nuclear attack was unwarranted for any other reason.

This veto option would be an important complement to the 25th Amendment, which can be used to remove the president from office if the vice president and a majority of the Cabinet believe he or she is physically or mentally “unable to discharge the powers and duties of his office.” Yet, implementing the amendment would take time, during which the president would retain the authority to order a nuclear attack.

Once in office, President Biden should also make a second, long-overdue change to U.S. nuclear policy: He should renounce the first-use policy of nuclear weapons.

U.S. policy has always included the option of using nuclear weapons first during a crisis. Over the decades, the United States has narrowed the circumstances under which it would consider doing so, but retains the option of using nuclear weapons first against three nuclear-armed nations — Russia, China and North Korea — practically guaranteeing a nuclear counterattack in the case of Russia or China.

Mr. Biden knows this policy should be changed. In 2016, as vice president, he said: “It is hard to envision a plausible scenario in which the first use of nuclear weapons by the United States would be necessary or make sense.”

President Biden should move quickly to implement these two policy changes — requiring the assent of two other officials to any nuclear launch order and eliminating the option of using nuclear weapons first. Doing so would make the world safer and demonstrate that the United States is committed to reducing the risk of nuclear use and to moving away from its reliance on nuclear weapons.

Lisbeth Gronlund and David Wright are research affiliates in the Massachusetts Institute of Technology’s Department of Nuclear Science and Engineering. From 2002 to 2020, they co-directed the Global Security Program at the Union of Concerned Scientists.