One of the reasons many Americans are growing increasingly wary of the United States intervening in sectarian armed conflicts in the Middle East is that our actions – no matter how well-intentioned – often have unpredictable consequences that produce more instability and volatility, fostering the conditions for terrorist organizations to thrive.

The United States’ ongoing involvement in the civil war raging in Yemen is a case in point.

After overthrowing the Yemeni government in 2014, the Houthis – a Shia Islam movement from northern Yemen – began an aggressive campaign to consolidate power in the country that included a moderately successful war against al-Qaeda in the Arabian Peninsula (AQAP), a rival faction vying for control in Yemen and also a sworn enemy of the United States. Of all the terrorist organizations operating around the world today, AQAP is consistently ranked by U.S. military and intelligence officials as one of the most dangerous and greatest threats to U.S. national security – a position that Secretary of Defense Ash Carter reiterated on Thursday in a hearing of the Senate Armed Services Committee.

Now, this doesn’t validate the old proverb that “the enemy of my enemy is my friend” – the Houthis are certainly not a friend to the United States – but there’s no denying that their string of battlefield victories against AQAP and their stated commitment to destroying the terrorist group coincided with one of the strategic objectives of U.S. military strategy in the Middle East.

But the Houthis’ successes – and AQAP’s losses – quickly came to an end when Saudi Arabia, a long-time ally of the recently overthrown Yemeni government, began attacking the Houthis more than a year ago. With its chief regional adversary dramatically weakened, AQAP was able to reassert itself and now controls a large portion of central Yemen and its coastline – an area that rivals the size of ISIS’s territories in Iraq and Syria.

And where did Saudi Arabia get the military equipment and logistical support necessary to carry out its extended intervention into Yemen’s civil war? The United States of America. In addition to providing hundreds of air-to-air sorties, the United States recently approved the sale of $1.15 billion worth of weapons to the Saudi military.

Now, there’s nothing wrong, in principle, with the United States government selling military weapons and equipment to our allies. Saudi Arabia has long been an American ally in a very volatile region, and strengthening that alliance should be a priority of our foreign policy in the Middle East.

But the fact that Saudi Arabia is an ally with whom we have a track record of selling arms is not a sufficient reason to endorse this arms deal. Yes, we want our allies to be strong and capable of defending themselves. And yes, we should offer them assistance in times of need. But the first and most fundamental responsibility of the United States government is not to satisfy the requests of our allies. It is to protect the lives and liberties of the American people.

Is intervening in the Yemeni civil war – and participating in the decades-long sectarian conflict underlying that war – necessary in order to protect the lives and liberties of the American people?

Earlier this week the Senate had an opportunity to debate this question in response to Senator Rand Paul’s resolution of disapproval of the billion-dollar arms sale to Saudi Arabia. But by voting to table Senator Paul’s resolution, the Senate opted the avoid this debate.

This was more than just a missed opportunity – it was a gross dereliction of duty. Members of Congress in both chambers have a responsibility to the American people to carefully evaluate our interventions abroad, and to participate in the process of defining America’s national interests and developing a foreign policy to pursue those interests. If we ever hope to earn back the trust of the American people, we must once again fulfill this obligation.