https://constitutioncenter.org/the-constitution/full-text

Article IV, Section 4 (full text)

The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.

What is a republic?

republic | rəˈpəblik |

noun

a state in which supreme power is held by the people and their elected representatives, and which has an elected or nominated president rather than a monarch.

Vote fraud PREVENTS (and is specifically INDENDED TO PREVENT) "the people" from electing their representatives.

PREVENTING (AND CORRECTING) VOTE FRAUD, INCLUDING FOR STATE ELECTIONS, IS A FEDERAL MATTER.