President Trump’s decision to order the killing of Iranian General Qassim Suleimani threatens to draw the United States even more deeply into a region that has already claimed too much American blood and treasure.

The international reaction was swift. Futures on global stock markets fell, and oil prices spiked, in anticipation of a wider conflict. In Iraq, where popular sentiment had once been building against Iranian influence in the country, that anger is now sure to be directed at the American presence, and thus constitutes a grave danger to Americans serving there and throughout the region. Writing before the Suleimani strike, Paul Pillar noted that American actions “have converted what had been a story of popular protests with an anti-Iran tinge into a story of strongly anti‑U.S. protests.” Now, as Jack Goldsmith observed (via the WSJ), “Iraqi Prime Minister Adel Abdul-Mahdi condemned the targeted killing as a violation of the terms underpinning the U.S. troop presence in the country.” So, the Iraqi government’s next move might be as important as Tehran’s.

But perhaps the most important reaction was among members of Congress who were incensed that the Trump administration would take actions that could result in a war with Iran without congressional authorization. Rep. Ro Khanna (D‑CA) took to Twitter last night to chastise those in the House and Senate who had voted for the National Defense Authorization Act that did not include language that would have blocked such an attack. Notably, that amendment had passed overwhelmingly in the House NDAA, and with bipartisan support. All eyes should be on Rep. Matt Gaetz (R‑FL), who cosponsored the amendment, and the other Republicans who voted for it, to see if they remain committed to the principle that Congress, not the President, has the authority to take the country to war.

Meanwhile, President Trump, who has hinted at his desire to end endless wars (even as he has presided over a dramatic expansion of nearly all of the conflicts that he inherited), now seems poised to add an enormous new one into the mix. Because, let’s be clear, while the United States and Iran have been locked in a cycle of confrontation for four decades, neither side has been prepared to engage in full-scale and direct conflict with the other. And yet that is a step that may very well follow from these actions — if cooler heads don’t quickly prevail. As ruinous as the war with Iraq has been — for the United States, for Iraqis, and for the people throughout the region — war with Iran would be far, far worse.

The title of our book, Fuel to the Fire, is tragically apt. President Trump inherited a broken foreign policy, and he has made it worse. John Glaser, Trevor Thrall, and I also point out the dangers associated with investing so much power in the hands of a man utterly unfit for the office of the presidency. America’s Founders anticipated this, too. But the system that they created has now been so thoroughly upended, that it will take concerted action across multiple fronts to stop this train that is hurtling down the tracks. And I worry that it might already be too late.