The arguments for and against the development of a competitive engine for the F-35 Joint Strike Fighter have been laid out countless times by opposing sides over the years this debate has raged. It is past time to make a decision and move forward.

And — especially with the recent decision by the second engine manufacturers to self-fund the next steps in engine development — the best decision for our fighting forces and the American taxpayer is to allow competition.

First, there is an unnecessary operational risk in having just one engine supply 90 percent of our fighter inventory. This program performance concern is reinforced by the experience of getting the principal engine for the F-35 (dubbed the F135) and its close relative the F119 (which is the name for the engine in the F-22) through all the many challenges in development. Furthermore, the design and outfitting of the Joint Strike Fighter will continue to evolve through the life of the program; if the aircraft gets heavier, that will increase its engine thrust requirements, and there are questions about the F135’s ability in this area.

Couple these issues with concerns over maintaining international interest in the program and the initial debate on whether there was ever a competition for the program. These issues have filled many Government Accountability Office studies, Defense Department analyses and independent assessments.

The benefits of having two viable engines for use in the Joint Strike Fighter are recognized by both sides in the debate, though the near-term costs were what deterred many from pursuing this goal. The latest announcement by the General Electric and Rolls-Royce team to self-fund the next steps in the development of its alternative F-35 engine (the F136) has changed this equation.

This bold move could mark the beginning of a new era in public-private partnerships in Defense Department contracting for the benefit of the taxpayer.

Even before this decision by the contractor, though, funding this engine development was a worthy investment. The benefits realized from effective competitions serve the best interest of both the warfighter and the taxpayer. I applaud Dr. Ashton Carter for his Better Buying Power initiatives to seek competition through all aspects of Defense Department programs. He is right that, when possible, head-to-head competition drives productivity and value. We should apply this principle to this large JSF investment.

Dr. Jacques Gansler, a respected former undersecretary of Defense, testified before Sen. Kay Hagan (D-N.C.) and me at an Armed Services subcommittee hearing this month on acquisition policies and the health of our defense industrial base. He addressed the clear differences in “competition for an award” as opposed to “competition during execution.” The former sets the stage for large cost growth from a monopolistic supplier, while the latter continuously lowers cost with concurrent performance and reliability improvements.

The often-cited Great Engine War of the 1980s provides many examples of the benefits brought about by engine competition during execution — from reduced costs, improved sustainment responsiveness and continuing advancements in performance and efficiency. As the centerpiece and workhorse of our nation’s multirole fighter inventory, our warfighters deserve to have the best equipment we can provide through the entire life cycle of the Joint Strike Fighter.

Engine competition cost savings estimates have varied. The most conservative estimates predict a break-even cost, while other estimates (including by the GAO) put the savings potential up to 20 percent — which would be at least $20 billion. What these assessments do not fully address is the savings achieved through increased contractor funding of development costs. Through all these assessments it is clear that, in the long run, developing and having the option to procure two competing engines is more cost-effective than pursuing only one.

It is true that we don’t have two engines for every major platform in the inventory. Sometimes it makes sense and sometimes it doesn’t. The question is whether an engine program of unprecedented size and cost can benefit from competition in execution, when there is a clear history of benefits to large engine contracts.

With the competitive engine at 80 percent completion and planned funding by the contractor, the decision is not a difficult one. Taxpayers deserve the continued benefits of competition in one part of the troubled Joint Strike Fighter program that is working well.

Sen. Rob Portman (R-Ohio) is one of two freshman Republicans on the Senate Armed Services Committee and is the ranking member of its Subcommittee on Emerging Threats and Capabilities. The alternate F-35 engine is being developed at a GE facility in the Cincinnati suburb of Evendale.