Imagine retiring after a long career serving in uniform, only to learn that your savings all those years had helped fund advanced weapons systems for America’s adversaries. This tragedy will soon become reality unless a decision by the Federal Retirement Thrift Investment Board is immediately reversed.

The FRTIB manages nearly $600 billion, making it one of the world’s largest retirement funds. Its Thrift Savings Plan is the federal-government equivalent of a 401(k), and any federal employee with a retirement fund through...