Ian Bassin is the executive director of Protect Democracy. He previously served as associate White House counsel to President Barack Obama.

Recently, Sen. Bob Corker (R-Tenn.) warned that he fears President Trump could lead us into World War III. On Monday, as chairman of the Senate Foreign Relations Committee, Corker can take an important step to prevent that.

At a hearing, he'll have before him Defense Secretary Jim Mattis and Secretary of State Rex Tillerson to discuss the administration's legal authority to conduct the global war on terror. Given Corker's concern that the administration could instigate an even broader war — whether with North Korea, Iran, or some other country with whom the president gets into an ill-advised Twitter spat — Corker should use the hearing not only to focus on the Authorization for Use of Military Force against the Islamic State and al-Qaeda (which is the scheduled topic) but also to set guardrails for the administration's use of force against any foreign power. As a start, he should press Mattis and Tillerson to explain precisely what this president thinks his authority is to launch a war without the explicit consent of Congress.

The organization Protect Democracy has been concerned about this question since the first time Trump ordered a military attack on a foreign government. When Trump launched military strikes against the Syrian regime this spring, we raised the question of what gave him the authority to do that: Congress had not authorized it; the United Nations Security Council had not authorized it; and the Syrian government had not attacked the United States. We asked the White House to disclose the legal justification for this strike, and then we sued to find out.

In July, Judge Christopher Cooper of the U.S. District Court in Washington ordered the administration to speed up its disclosures on the information we requested because, as he explained in a striking opinion, the decision of whether to go to war is one that requires a public debate and "being closed off from such a debate is itself a harm in an open democracy." With the administration's actions and words suggesting possible escalation of military adventurism, speed in having such a debate was important, he wrote, because "military strikes cannot be undone."

In response to the judge's order, the administration revealed that a legal memorandum does exist that ostensibly advised the president on what authority he did or did not possess to strike the regime of Syrian President Bashar al-Assad. The Justice Department reports that they believe the memo was prepared on April 6, the day of the strikes, but they are refusing to disclose the memo. What does it say? Does it say the president did have the authority to launch those strikes? Does it express that the lawyers had reservations about his authority? Did the president consult it prior to acting or was it written as a post hoc justification after the strikes were ordered?

Because the administration has continued to refuse to disclose what the president thinks his authority to take us to war is, on Thursday, we filed a new lawsuit to find out whether the president's lawyers think he can unilaterally start a war with North Korea.

The Constitution assigns Congress a key role in deciding when our country goes to war. Few would disagree that presidents and legislators of both parties have shifted these war-making powers away from the careful balance the Founders laid out in the Constitution. But this president's words and actions suggest he has an even more extreme approach that is an acute danger to our democracy and security. We are now faced with the circumstances that led the Founders to place the power of declaring war in the hands of Congress, not the president.

While the president is entrusted with the command of our armed forces and the responsibility of national security, history suggests we are a stronger nation and more successful on the battlefield when the American people have a say in declaring war. While some argue that Congress should be sidelined when it comes to a first strike in order to preserve unpredictability, that argument is far outweighed by the unfathomable potential downside. A "surprise" military strike against North Korea, without Congress, could lead to a "surprise" nuclear war for the American people. That is as far from the intent of the Founders and plain language of the Constitution as one could imagine.

Put simply: Congress must act. Corker has an opportunity to begin to do so. And he is not alone. Sen. Tim Kaine (D-Va.) and Rep. Adam Schiff (D-Calif.) have raised alarms about Trump's view of his war-making authority for months. Rep. Ted Lieu (D-Calif.) and Sen. Ed Markey (D-Mass.) have introduced legislation that would require congressional approval for any nuclear first strike anywhere. Sens. Chris Murphy (D-Conn.), Brian Schatz (D-Hawaii) and Cory Booker (D-N.J.) announced plans to introduce a bill requiring congressional authorization before any preemptive strike of any kind against North Korea — a requirement with which Republican Sen. Dan Sullivan (Alaska) agrees. And Sens. John McCain (R-Ariz.) and now Jeff Flake (R-Ariz.) have taken the important step of making clear that even members of the president's own party will no longer be complicit in his recklessness.

This is a president who seems to believe he is above any constraint whatsoever in war-making — that, as Senior Advisor Stephen Miller put it, his powers "will not be questioned." That is not how the Constitution works. On Monday, it's time for Congress to start the questioning.