I'm sorry, but the provided answer is incorrect. The Constitutional provision that allows protestors to gather on the National Mall to protest lack of civil rights is the First Amendment to the United States Constitution. The First Amendment guarantees the right to freedom of speech, assembly, and petition. This means that individuals have the right to peacefully assemble and protest in public spaces like the National Mall to address grievances and advocate for civil rights. The First Amendment plays a crucial role in protecting the rights of citizens to express their views and participate in democracy through peaceful demonstrations.