Federal law generally prohibits disenfranchisement of people based on race, age, national origin, sex, marital status, disability, pregnancy, gender, sexual orientation and disability, along with other categories.
Federal law does not prohibit disenfranchisement based on ideology, political affiliation or outlook. If a state or local election system wants to block voters based on affiliation or ideology, they can…. as long as it doesn’t have a disparate impact on the protected category.
If a state legislature wanted to assign 1/2 value to each Republican vote, there is nothing in the constitution that would prohibit that rule.
If a state election outcome results in the loss of 50% of the republican votes in the local or state election, there is nothing in the federal law that would correct the issue. The state is responsible for certifying the results.
The supreme court will not hear an election controversy issue or legal challenge based on certified results from states. The constitution permits states to conduct their own elections, and as long as federal laws are not violated, the state certification ends the discussion. This is the great dichotomy within U.S. election around election manipulation by a state or local election officials. There is no federal recourse if no federally protected category was adversely impacted.
The DNC argues election disenfranchisement, rules, dates, times, locations, etc based entirely on protected federal categories, ie. the date or method of the election has an adverse impact to a specifically protected category of racial minorities. This is the typical DNC lawsuit.