Saudi Arabia has suffered attacks from Iranian launched or provided missiles from both the north and south, and its capital has been repeatedly attacked with ballistic missiles. The war in Yemen has spun out of control so much that Saudi security is more endangered now than it was at the start of Saudi Arabia’s intervention in 2015. Yet, as the kingdom faces mounting insecurity, it has alienated most of its security guarantors and weapons suppliers in the West, which are increasingly concerned over the humanitarian crisis in Yemen and remain outraged over the 2018 killing of Saudi journalist Jamal Khashoggi.

Politicians in Canada, Germany, and the United Kingdom have all proposed restricting weapons exports to Saudi Arabia. In the United States, there are the beginnings of a bipartisan consensus against additional weapons sales to the kingdom. Even during the administration of former President Donald J. Trump, the secretary of state had to invoke a rarely used provision for emergency sales to prevent congressional disapproval of key weapons sales to Saudi Arabia and the United Arab Emirates.

Joseph R. Biden Jr., as a presidential candidate, was unequivocally negative about Saudi Arabia. He stated in a debate that he believed Crown Prince Mohammed bin Salman personally ordered the murder of Khashoggi, and Biden said he would stop weapons sales to the kingdom. As president, Biden has changed his posture. While he has avoided meeting or speaking with the crown prince, the responsibilities of the office have moderated his position on U.S. security assistance to the Saudi Arabia. In the first few months in office, Biden’s administration announced a “recalibration” of the relationship that would seek to rein in the worst aspects of Saudi behavior, appoint a special envoy to broker an end to the Yemen war, and prevent Saudi Arabia from realigning its security away from the United States by continuing to supply “defensive” weapons.

So far this package of measures seems to have partially mollified the Saudis, even if the measures have irritated some in the president’s own party. It appears that, politically, U.S.-Saudi relations have found a level of stasis, albeit on terms that the Saudis view as less than favorable.

The problem with only providing “defensive” weapons is that Saudi security conditions are continuing to deteriorate. The distinction between “offensive” and “defensive” weapons doesn’t exist in military doctrine; this is more of a political than a military delineation. In March, there was a complex drone and missile attack on Aramco facilities in Dhahran; Iranian missiles continue to be fired from Houthi positions in Yemen into Saudi Arabia’s interior; and there are near constant drone and missile attacks into southern Saudi Arabia from Yemen. The United States’ special envoy for Yemen, Timothy Lenderking, has stated that over 300 attacks have been launched into the kingdom in the last year alone.

The Saudi defense forces have a strong record of defeating these attacks – indeed, the Royal Saudi Air Defense Forces is the world leader in ballistic missile intercepts. The U.S. Patriot missile system that has been used to intercept all of these missiles and many drones has been patiently built up over a generation and is considered by some the most effective branch of the Saudi armed forces. The Saudi Air Defense Forces have managed to integrate U.S. and Greek Patriot systems into their operations. Tactically, the Saudis have actually improved upon U.S. practice for intercepting missiles, for example by requiring additional operators to discern targets prior to launch.

But this efficacy comes at a substantial cost. Missile defense – in effect hitting a bullet moving through the sky at supersonic speeds with another bullet – is an extremely expensive undertaking. Frequently used metaphors – such as “shield” or “dome” – are misleading. Missile defenses are really point defenses, capable only of defending limited high-value areas against a few incoming missiles. The Saudi success comes from firing at least two Patriot missiles – which cost the Saudis an estimated $3 million to $4.3 million each – at each target. The incoming missiles, predominantly Iranian made, cost a fraction of this; drones cost even less, probably less than $20,000. Air defense systems, such as the Patriot as well as the Russian S-400, are not designed to provide stand-alone comprehensive defense by themselves but only to protect key facilities until a counter strike can be directed against enemy launch sites.

The September 2019 attacks on oil processing facilities in Abqaiq and Khurais, widely attributed to Iran, showed another problem. Drones were launched from north of the kingdom into the interior of Saudi Arabia and then shifted to attack the facilities from a direction that was unmonitored and undefended. Because drones tend to fly at low altitude, they might have been undetected even if the Patriot radar had been aligned to protect the refineries from missiles.

As mentioned, drones cost a fraction of ballistic missiles – and using an expensive system such as the Patriot (or even cheaper rivals such as the S-400) against drones is a losing economic proposition (although thus far, the Saudis have demonstrated the ability to absorb the costs for deploying the Patriot system). The Saudi air force has been using cheaper advanced medium range air-to-air missiles, or AMRAAMs, to engage drones in flight, but this is also an expensive proposition. The Saudis operate from a place of financial strength and may view this exchange (expensive missiles versus inexpensive drones) as acceptable, but it also means the Saudis are expending their inventory of (U.S.-procured) missiles more rapidly than planned.

And, of course, all of these missiles are manufactured in the United States and sold to the Saudis. The current problem is that the kingdom is running out of missiles.

On the face of it, this should not present a major problem for the Biden administration. If there is such a thing as a “defensive” weapon, the Patriot certainly fills the bill – it is a surface-to-air missile, the most modern variant (called PAC 3) has an inert warhead and thus can’t be converted into any reasonable surface-to-surface role, and it is in the front line of defending against ongoing (and indiscriminate) attacks against Saudi cities, including an attack on Riyadh in early December. Providing additional Patriot missiles and AMRAAMs would seem to be well within Biden’s stated aim to provide Saudi Arabia with “defensive” weapons.

However, there is a significant cleavage with the president’s congressional party. In November, he notified Congress of his desire to replenish Saudi Arabia’s AMRAAM inventory. This should have been an easy one – these are air-to-air missiles and thus have not been used in any attacks in Yemen, and clearly fall within the framework set by the president. But opponents of the sale introduced a measure of disapproval (which is relatively rare) and managed to get 30 senators to vote for it, though not enough support to pass the measure. While it is possible that at least some of these votes against the sale were tactical – knowing the sale was likely to pass, they chose to appeal to their base – this is a worrying precedent.

If Congress were to take action to stop the sale, it would have to pass a joint resolution of disapproval with enough votes to overrule a presumed presidential veto. This is unlikely. However, the possibility of a congressional vote with floor speeches decrying Saudi behavior in a variety of areas is not something the Saudis – or the White House, for that matter – would relish. The Biden administration may take advantage of the congested congressional calendar to move quickly to process the sale, hoping to keep any action off the calendar.

Regardless, most Patriot equipment and missiles are sold to the kingdom not via the U.S. government foreign military sales system but rather as commercial sales. This means that a license – which is good for up to four years – is granted to the exporting company, and then there is no further routine congressional review until the license expires. So, for example, in recent months the kingdom has purchased over 100 Patriot PAC 2 missiles (those with an exploding warhead, rather than an inert one as in PAC 3) without any congressional notification.

Now the Saudis have applied to replenish the rest of their stores of Patriot missiles. In theory, this also should be easy – it is harder to think of an offensive role for Patriot missiles than it is for AMRAAMs – but the level of dissatisfaction with the kingdom in Congress is at unprecedented levels. Nevertheless, it would be damaging for the United States’ credibility with its allies and partners if the multibillion-dollar Saudi air defense system – consisting of a very expensive network of launchers, radars, combat control systems, and support equipment – were to become nullified by a shortage of missiles.

In any event, the ideal solution down the road to Saudi Arabia’s weapons challenges is to work with its neighbors to achieve a state where missile defenses aren’t needed. The continental United States has no Patriot batteries on homeland defense alert: Should the various Yemeni negotiations meet with success, the kingdom may be able to step back as well and have less need to expend missiles.