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

While the Constitution gives the States the provisional right to prescribe the "Times, Places and Manner of holding Elections for Senators and Representatives" -- provisional as described below in Article I Section 4 -- later in the document, Article IV Section 4 makes clear that the FEDERAL government has the duty to "guarantee to every State in this Union a Republican Form of Government", which is to say, to guarantee that elections are A) held and B) HONEST.

Vote fraud's entire purpose is to disenfranchise citizens, and the FEDERAL GOVERNMENT is Constitutionally charged with preventing such fraud, however it might be attempted or achieved.

Article I Section 4: Elections

The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof; but the Congress may at any time by Law make or alter such Regulations, except as to the Places of chusing Senators.

Article IV, Section 4

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.

Dictionary definition:

republic | rəˈpəblik | noun

a state in which supreme power is held by the people and their elected representatives