The Trump administration has, for the first time ever, built a searchable national citizenship data system.

The tool, which is being rolled out in phases, is designed to be used by state and local election officials to give them an easier way to ensure only citizens are voting. But it was developed rapidly without a public process, and some of those officials are already worrying about what else it could be used for.

NPR is the first news organization to report the details of the new system.

For decades, voting officials have noted that there was no national citizenship list to compare their state lists to, so to verify citizenship for their voters, they either needed to ask people to provide a birth certificate or a passport — something that could disenfranchise millions — or use a complex patchwork of disparate data sources.