As lawmakers in Washington appear at least a little closer to authorizing new military aid to Ukraine, Taiwan and Israel, the questions over whether the US industrial base has the capacity to meet the global demand for American arms have only grown louder.

Even prior to the war in Gaza, the US was beginning to experience a weapons overlap between platforms destined for Kyiv and those destined for Taipei. If Congress approves Biden’s request for additional Ukraine aid, the tradeoff between arming Ukraine and Taiwan will become more important in 2024 and beyond.

Discussion around the tradeoffs between arming Ukraine and Taiwan have coalesced around two schools of thought. There are the optimists, including senior US and Taiwanese officials, downplay the overlap between Ukraine and Taiwan, and argue that more support for the former does not negatively impact the latter. Then there are the pessimists contend that continued support for Ukraine could worsen a large backlog of US weapons earmarked for Taiwan. Pessimists further argue that arming Taiwan is the greater strategic imperative.

I am a pessimist and believe that if not now, soon enough the US will have to make hard choices about how best to support two beleaguered friends with finite resources. It should, for one, consider freezing new foreign military sales to European allies in order to European industry to take on more of the burden while the US focuses on Taiwan.

Most US military aid to Ukraine so far has come through different legal and funding mechanisms than arms sales to Taiwan, and thus does not currently create a tradeoff. This picture will change, however, as US defense production lines will have to make new weapons that are due to Taiwan, Ukraine, NATO states, and other allies and partners. These longer-term demands on US defense industry are a ticking time bomb.

There are three specific pressure points: foreign military sales (FMS) to NATO states; a growing number of overlapping weapons covered by the Ukraine Security Assistance Initiative (USAI); and the increasing number of overlapping weapons sent to Ukraine through presidential drawdown authority (PDA) that will need to be backfilled.

Nearly all US arms sales to Taiwan are done via FMS. Weapons sold through FMS are built from scratch and subject to a lengthier review process. According to the Stockholm International Peace Research Institute, across deliveries to all clients completed between 2012 through 2021, the average time between sale announcement and delivery was about four years for air defense systems, three-and-a-half years for aircraft, and two-and-a-half years for missiles. Sometimes, however, these delays stretch up to almost 10 years.

Currently, Taiwan is waiting for delivery of approximately $19 billion worth of weapons that the US has sold using FMS. Since the start of Russia’s invasion in February 2022, Washington has only announced two arms sales to Ukraine using the FMS mechanism, and neither of these sales were for capabilities in the Taiwan arms backlog.

While there is no Ukraine-Taiwan weapons overlap in FMS, the overlap between Taiwan and other US allies, particularly NATO states, has grown considerably since the war in Ukraine started. Since February 2022, there have been 121 FMS announcements, six for Taiwan. Just shy of half of the remaining sales (55 out of 115) contain at least one weapon system that overlaps with Taiwan’s backlogged weapons. NATO member states account for 53 percent of overlapping sales (29 out of 55).

US aid for Ukraine furnished through USAI will also place long-term stress on US production lines, albeit over a shorter time period. USAI funds are used to create contracts with US defense industry to build new weapons and other supplies for Ukraine. This means that delivery of USAI capabilities is on a longer timeline than PDA, but a shorter timeline than FMS. According to a senior US defense official in August 2022, USAI-provided weapons could take months or a few years to arrive in Ukraine.

Of the 17 USAI announcements made since February 2022, 10 contain at least one capability that overlaps with Taiwan’s backlogged weapons. This overlap is mostly for munitions, but it includes some big-ticket items including the HIMARS rocket artillery system, land-based Harpoon missiles, and the NASAMS air defense system. Taiwan ordered HIMARS and Harpoon via FMS in October 2020, but full delivery is not expected until 2026 and 2028, respectively. While Taiwan has not yet ordered NASAMS, press reports from 2023 indicated that both the US and Taiwan governments are interested in a sale, which could occur in 2024.

The final area of concern for the Ukraine-Taiwan overlap is the growing number of stockpiled weapons that Ukraine receives through PDA. According to a December 2023 State Department fact sheet, the United States has sent Ukraine $23.8 billion in PDA over 44 transfers since August 2021. Taiwan is also eligible for PDA and received a $345 million shipment in July 2023.

While the current Ukraine-Taiwan PDA overlap is small, replenishing US equipment transferred to Ukraine could add to existing production stress. Washington is spending money to speed up replenishment, but building additional production capacity takes time. Moreover, even if production lines are expanded, Taiwan could still find itself near the back of the line in terms of weapon delivery priority, as it must compete against US stockpile replenishment, Ukraine USAI sales, and other FMS customers.

The tradeoff between arming Ukraine and Taiwan has been manageable but is worsening. The overlap between weapons owed to Taiwan, FMS announcements to bolster European security, USAI equipment that has yet to be produced, and weapons sent to Ukraine via PDA that the US military must replenish is steadily growing.

There are several policy actions Washington should take to navigate the Ukraine-Taiwan weapons overlap.

First, the United States should refrain from announcing more FMS sales to NATO states to free up US defense industrial capacity and incentivize greater European industrial base investment. The United States is already on the hook for plenty of weapons to NATO countries. No new FMS sales to NATO states for a period of several years will give the US industrial base time to fulfill existing orders while providing incentives and time for European states to increase spending on their own industrial capacity.

Second, the United States should do more to encourage weapons co-production with Taiwan. If Taiwanese companies can build US weapons under license, either partially or in full, then it should speed up the delivery of backlogged weapons. Moreover, co-production will provide opportunities for Taiwan’s defense industry to gain experience and increase capacity, which should aid the production of indigenously designed weapons.

Finally, the United States needs to have difficult discussions with Ukraine about the limits of US military aid. The Biden administration’s repeated statements about open-ended support are running into a circumspect Congress that is hesitant to keep the spigot open indefinitely. This political friction is compounded by serious concerns about the US industrial base capacity. American support for Ukraine may look very different, and less expansive, in 2024 than it did the two previous years.