DENVER (AP) — A liberal group has filed a lawsuit to bar former President Donald Trump from the primary ballot in Colorado.

The lawsuit contends Trump is ineligible to run for the White House again under a rarely used clause in the U.S. Constitution aimed at candidates who have supported an “insurrection.”

The lawsuit, citing the 14th Amendment, is likely the initial step in a legal challenge that seems destined for the U.S. Supreme Court.

The lawsuit was filed on behalf of six Republican and unaffiliated Colorado voters by the group Citizens for Ethics and Responsibility in Washington.