Early uses of Section 3 were just that Congress refused to seat ex-Confederates who had been elected to the House. The point is that there was no requirement for a statute to be passed by Congress that they had that power, or that some court first needed to declare the incoming reps as insurrectionists.
On the broader question of whether Section 3 is "self-executing," I here quote from a persuasive article by Mark Brown, a law professor at Capital:
"Section 1983 was passed in 1871 to correct state and local abuses of freed slaves throughout the Reconstructed South. It awarded, and still awards, the victims of unconstitutional conduct a private action against the offending government official. It has in modern times (defined as since 1961) become the premier mechanism for vindicating federal wrongs perpetrated by state and local officials.
"But before modern developments beginning in 1961, constitutional provisions (including those in the Fourteenth Amendment) were always understood to be enforceable without federal enforcement statutes like section 1983. As explained by Professor Anne Woolhandler, “positive,” “direct,” “offensive” constitutional litigation in state and federal courts long preceded the adoption of the Fourteenth Amendment in 1868, section 1983 in 1871, and general federal question jurisdiction in 1875. “Throughout the nineteenth century, both before and after Reconstruction,” she explains, “the Court saw diversity jurisdiction as an appropriate vehicle to raise federal questions, sometimes providing an expansive scope to diversity explicitly to accommodate this use of it.” Consequently, “much of the Supreme Court’s development of individual rights and remedies took place without reliance on either federal question jurisdiction or statutes such as § 1983, but rather under the rubric of diversity jurisdiction.” Congressional enforcement mechanisms and federal question jurisdiction did not exist, were not used and were unnecessary. Constitutional provisions were fully enforceable without congressional assistance."
Early uses of Section 3 were just that Congress refused to seat ex-Confederates who had been elected to the House. The point is that there was no requirement for a statute to be passed by Congress that they had that power, or that some court first needed to declare the incoming reps as insurrectionists.
On the broader question of whether Section 3 is "self-executing," I here quote from a persuasive article by Mark Brown, a law professor at Capital:
"Section 1983 was passed in 1871 to correct state and local abuses of freed slaves throughout the Reconstructed South. It awarded, and still awards, the victims of unconstitutional conduct a private action against the offending government official. It has in modern times (defined as since 1961) become the premier mechanism for vindicating federal wrongs perpetrated by state and local officials.
"But before modern developments beginning in 1961, constitutional provisions (including those in the Fourteenth Amendment) were always understood to be enforceable without federal enforcement statutes like section 1983. As explained by Professor Anne Woolhandler, “positive,” “direct,” “offensive” constitutional litigation in state and federal courts long preceded the adoption of the Fourteenth Amendment in 1868, section 1983 in 1871, and general federal question jurisdiction in 1875. “Throughout the nineteenth century, both before and after Reconstruction,” she explains, “the Court saw diversity jurisdiction as an appropriate vehicle to raise federal questions, sometimes providing an expansive scope to diversity explicitly to accommodate this use of it.” Consequently, “much of the Supreme Court’s development of individual rights and remedies took place without reliance on either federal question jurisdiction or statutes such as § 1983, but rather under the rubric of diversity jurisdiction.” Congressional enforcement mechanisms and federal question jurisdiction did not exist, were not used and were unnecessary. Constitutional provisions were fully enforceable without congressional assistance."
https://www.jurist.org/features/2023/10/12/trump-and-section-3-of-the-fourteenth-amendment-an-exploration-of-constitutional-eligibility/