For more than 75 years, U.S. nuclear forces have underpinned American power and kept our homeland safe. The Soviets understood our stockpile’s potential, which kept them from moving against us. That stockpile has deterred a host of other enemies since.

This makes the preservation of our nuclear shield nonnegotiable. But critical updates to our arsenal are underfunded and behind schedule. Congress and the White House must act quickly to solve these problems and prevent more from emerging.

Over the past decade, the Defense and Energy departments have developed replacements for our Cold War-era nuclear forces. Chief among them is the Sentinel intercontinental ballistic missile. This new weapon would replace the nearly 60-year-old Minuteman III ICBM and its supporting infrastructure, both of which are almost obsolete. The Sentinel would not only be more capable and resilient than the Minuteman III, but also easier to maintain and upgrade.

This replacement has proved easier said than done. On Jan. 18, the Pentagon notified Congress that Sentinel breached its Nunn-McCurdy cost threshold. In other words, the program would be over budget.

Sentinel would be the largest U.S. government civil works project since the completion of the interstate highway system in the 1990s. Drawing on initiatives from more than 50 government agencies and across 45 states, it is the most complex acquisition program the Air Force has ever undertaken.

Attempting anything on such a scale is fraught with risk, so the Air Force’s announcement that Sentinel is suffering cost overruns and potential delays isn’t surprising. For a decade, defense experts have cautioned about the logistical, technical and resourcing challenges facing the necessary replacement for the Minuteman III.

Sentinel might have weathered such challenges if defense planners and the White House had handled them appropriately. Yet President Biden, like many previous administrations, ignored the relevant warnings. On the campaign trail, Mr. Biden and his advisers were hostile to nuclear modernization,vowing to eliminate critical programs and enact policies that would have undercut U.S. credibility with allies. China’s buildup, Russia’s continued aggression, and North Korea’s and Iran’s nuclear ambitions have kept the president’s advisers from deserting the rebuild. They are, nevertheless, playing political games that cost time and money. The administration remains stubbornly unwilling to prepare for a world in which we face not one but two peer nuclear adversaries.

Satellite imagery reveals that China has built more than 300 new ICBM silos since at least 2021—more than the U.S. has constructed in the last five decades. Beijing has tested a new weapon capable of orbital nuclear attacks with almost no warning and set a pace to exceed the size of the U.S. nuclear arsenal by 2030. Russia already commands the world’s largest nuclear force. It is now fielding heavy ICBMs of almost unlimited range. The Kremlin also boasts a 10-to-1 advantage over the U.S. in shorter-range tactical nuclear weapons, as well as intercontinental-range nuclear-powered torpedoes and cruise missiles.

Unfortunately the Biden administration’s economic policies and anemic military support have forced Sentinel—and all our urgently needed modernization efforts—to overcome staggering inflation and a lack of crucial technology suppliers, skilled labor and raw materials. As suppliers struggle to guarantee a steady low-cost supply of steel and cement, the costs of Sentinel will rise dramatically. This administration, including the Pentagon, had ample opportunities to encourage innovation, demand program performance, and push for expanded domestic industrial capacity.

Despite these challenges, abandoning or downsizing Sentinel isn’t an option. Our nation’s safety and prosperity depend on an updated and fully operational nuclear deterrent.

As the ranking members of the Senate Armed Services Committee and the Strategic Forces Subcommittee, we will use all congressional oversight tools to maximize taxpayer investment in the Sentinel program. Expanding training for skilled workers, applying the Defense Production Act to broaden construction commodity availability and stabilize inflation, and restoring America’s position as the global hub for manufacturing innovation all would receive bipartisan backing.

We must hold the administration accountable for its failures. But to make up for decades of neglect, our colleagues in Congress must also commit to restoring U.S. industrial health and developing the workforce required to keep America’s nuclear forces armed and ready for any challenge.

Mr. Wicker and Ms. Fischer, both Republicans, are U.S. senators from Mississippi and Nebraska, respectively.

This op-ed originally appeared in the Wall Street Journal. Read it here.