The writer, a Republican, represents Michigan’s 8th District in the House, where he serves as chairman of the intelligence committee.

Twenty-five years ago Saturday, Iraqi dictator Saddam Hussein unleashed chemical weapons on his own citizens, killing thousands of innocent men, women and children in the Kurdish town of Halabja. As we remember that horror and reflect on the lives ended by a tyrant, we must realize the world is on the brink of witnessing a similar atrocity in Syria. Once again, we may see images of dying mothers vainly shielding their infants from the chemical storm.

For too long, the regime of Bashar al-Assad — backed by Iran and helped by the Lebanese militant group Hezbollah — has been free to cross red line after red line as it kills and wounds tens of thousands of Syrians. With little to no response coming from the United States over the past two years, the world has waited for the leadership necessary to halt Assad’s murderous acts. And as Syria unravels, the vacuum created by absent U.S. leadership is filling with extremists such as Jabhat al-Nusra, a Syrian terrorist group affiliated with al-Qaeda that seeks to undermine the secular uprising’s goals for greater liberty.

These events play out in the shadow of Assad’s inventory of chemical weapons. As domestic disorder escalates and the Assad regime becomes more eager to regain control, public reports suggest that the regime may be preparing to use chemical weapons. When it comes to chemical weapons, we must be clear and unequivocal: If the United States receives credible intelligence that the Assad regime is using — or preparing to use — chemical weapons against the Syrian people, we will respond with swift and devastating military force.

Before that happens, we must renew our efforts to create a more stable Syria. It is clear that the current U.S. approach — focusing on diplomatic pressure and economic sanctions while offering next to no military assistance — simply has not worked. For far too long, the United States has ignored pleas for military aid and avoided opportunities to shape both the nature of the Syrian opposition and the direction of this conflict. Because of this passivity, our allies and the Syrian opposition are skeptical of our support and credibility.

In the absence of U.S. leadership, others have stepped into the void and provided assistance and weapons that are now more likely to fall into the wrong hands and fail to earn the United States any influence or goodwill. Our absence undermines our ability to effect positive change in Syria.

To have a role, we must be present. And to be credible, the United States must back up our call for the end of the Assad regime with tangible support for key players, including providing better coordination among opposition groups and the selective arming of U.S.-trained opposition members. In conjunction with our allies, we should consider implementing a safe zone in the north where we can better identify and organize opposition groups, give refugees safety and allow rebel fighters to remain in their country as they train and equip. We should also move to confront the threat that Assad’s Scud missiles pose to Syrians and people in neighboring countries, including by deploying the Patriot PAC-3 anti-aircraft and missile units based in Turkey.

Such steps do not include the use of conventional U.S. forces, but may include small groups with specialized capabilities. We must be willing to put force behind our diplomatic efforts if we hope to encourage any sort of positive outcome. For some time, Iran, Hezbollah and others have been throwing their weight behind Syrian proxies who pose a threat to the United States and its allies.

Assad’s intention to use — or his actual use of — chemical weapons is a red line that the United States must be prepared to enforce. We must do all we can to prevent another atrocity like the one that happened 25 years ago.

Read more on this issue:

John B. Bellinger III: What may compel U.S. intervention in Syria

The Post’s View: Syria’s bloody anniversary

Stephen J. Hadley: Steps for a more active U.S. policy in Syria

Zalmay Khalilzad: What the U.S. should do in Syria