President Donald Trump committed an impeachable offense this week, but you likely haven’t heard about it on cable news.

It did not involve firing the director of the FBI, nor conspiring with the attorney general to facilitate the firing that even some Republicans recognized as a potential obstruction of justice, nor bragging to the Russians about how “pressure” was “taken off” by that firing, nor any of the other acts of presidential maladministration that scream out for an accountability moment.

Those developments may have gotten the impeachment clock ticking faster, as Wisconsin Congressman Mark Pocan suggested. But there was another event—nothing to do with Russia—that should have set off the alarm: Donald Trump’s refusal to respect the requirements that the US Constitution places on presidents when it comes to matters of war and peace.

On Wednesday, US forces carried out more unauthorized air strikes on pro-government forces in Syria. Though the Constitution explicitly states that the legislative branch, not the executive, has the power to initiate new military actions, Trump has steered the United States deeper into the Syrian conflict.

After initial reports that US officials had confirmed “that the US-led Coalition hit Assad regime forces with air strikes in southern Syria today,” Congressman Ted Lieu, a former active-duty officer in the US Air Force now serving as a colonel in the Reserves, who is an expert in military law, had the right response on Twitter:

If true, this is FRICKIN ILLEGAL. Trump does not have Congressional authorization to attack Syria, a country that has not attacked US. https://t.co/5cf7gBVwC7

—Ted Lieu (@tedlieu) May 18, 2017

The congressman later issued a statement:

For the second time in as many months, the US military has conducted airstrikes against pro-Assad forces in Syria. The Trump Administration does not have congressional authorization to carry out military strikes against the Assad regime. Furthermore, the situation that led to today’s strike is precisely why I warned against getting further entangled in the Syrian civil war without a clear strategy. President Trump needs to explain his plan for Syria to Congress and the American people.

Lieu is not alone in expressing concern about this undeclared war making. After Trump ordered military strikes on Syria in April, Congressional Progressive Caucus leaders Raúl Grijalva, Keith Ellison, and Mark Pocan released this statement:

In the absence of an imminent threat to the United States, the president must seek Congressional authorization prior to any act of war. Trump failed to seek, much less gain, Congressional authorization. If President Trump believes that US military actions should be utilized against the Assad regime, he should immediately call the House and Senate back into session to debate and vote on the use of military force. These unauthorized attacks could pull the United States into a regional war and escalate this unprecedented humanitarian crisis.

Even Republican Congressman Justin Amash said in April, “Airstrikes are an act of war. Atrocities in Syria cannot justify departure from Constitution, which vests in Congress power to commence war.” Republican Senator Rand Paul called on Trump to “come to Congress for a proper debate.”

Trump did not answer the call.

Rather, the commander in chief is presiding over the unauthorized expansion of US military involvement in Syria—and disregarding the Constitution’s most serious dictates regarding war and peace.

The commentariat can and will debate when a president’s refusal to seek congressional authorization for military action becomes impeachable. (There will even be attempts by the apologists for presidential overreach to make convoluted claims about how past authorizations of the use of military force somehow apply to every new conflict.) But, in Trump’s case, there is no evidence to suggest that he will respect the requirements of the Constitution. As such, an article of impeachment is justified.

Of course, impeachment is a political process rather than a legal one. It requires a level of respect for the Constitution that is rarely evidenced by leaders of the House or the Senate—especially ones like Paul Ryan and Mitch McConnell. But political processes evolve when popular pressure rises—and it is worth noting that public support for impeachment is higher among voters than on Capitol Hill. Indeed, the new Public Policy Polling survey finds 48 percent of Americans want Trump impeached, while just 41 percent oppose impeachment. There’s no reason to think he won’t keep providing justifications.