The first political demonstration I ever attended was against the Iraq War. I was in middle school when the invasion started, and I still have trouble wrapping my head around its costs. The medical journal Lancet estimated in 2006 that this war caused the deaths of 655,000 Iraqis. Around 4,500 U.S. service members were also killed in Iraq; more than 32,000 were wounded. And that only accounts for physical injuries. The mental injuries were also tragic: Four times more veterans from Iraq have died by suicide than were killed in active operations. These are the consequences of morally injurious wars.

The political fallout from this catastrophic conflict may have been equally significant. The vast majority of Americans eventually came to believe that the war was not worth fighting. This dynamic has had a huge impact on U.S. elections. Barack Obama’s opposition to the Iraq War arguably won him the 2008 Democratic nomination and absolutely contributed to his huge general election victory that year. The issue also played an outsize role in Donald Trump’s takeover of the Republican Party; in 2016 Trump used Iraq as a sledgehammer to dispatch Jeb Bush before weaponizing it again to attack Hillary Clinton.

Lesson learned: Clearly, unpopular wars have enormous potential to profoundly remake American politics—to shatter a staid status quo and elevate change agents above political insiders. The world-shaping impact of a military mishap is something that should be on the forefront of every Democratic elected official’s mind as the Trump administration moves closer to enmeshing itself in Trump’s own disastrous misadventure by joining Israel’s recently launched war on Iran.

Putting aside the moral and geostrategic considerations that cry out against such an entanglement, it is clear that American participation in this conflict has the potential to be a massive political boondoggle for Donald Trump. Asked in a recent poll if the U.S. military should get involved in Israel’s war with Iran, 60 percent of........

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