What's at stake in Supreme Court battle over controversial legal theory about who controls...

The U.S. Supreme Court is set to hear arguments in its coming term on the legitimacy of a controversial legal theory about who oversees elections and whether that authority has limits.

The “independent state legislature" theory, backed by a group of conservative advocates, contends that state lawmakers have the ultimate power to regulate federal elections. That power of elected representatives, the theory's supporters argue, isn't subject to the traditional restrictions provided by state constitutions, state courts and governors' vetoes.

But the theory, if embraced by the justices in its most extreme application, could have a dramatic impact on how congressional maps are drawn, voting rules are written and more, according to election experts who spoke with ABC News.

The theory could undermine how American democracy works now, these experts said, raising concerns about what it could mean for how the 2024 presidential race and other contests are run.