It may seem strange but the Constitution does not guarantee a right to vote. Voting is implicitly set out in the Constitution. Article 1, for example, describes the manner or electing Representatives, which implies that they are elected by the votes of the people. The Nineteenth Amendment gives women the right to vote, and the Twenty-Sixth Amendment lowers the voting age to eighteen. But the Constitution never explicitly states that the people have the right to vote, and under the current dominant theory of Constitutional interpretation (known as Textualism and Original Intent) if a provision is not explicit it is suspect and not fully constitutionally protected. Because of this, Congress and state legislatures frequently set up road impediments to voting.
A Constitutionally guaranteed right to vote would not only ensure that citizens have that right, it would give citizens the ability directly challenge laws attempting to disenfranchise them. It would also force Congress to enact legislation to ensure that voting rules are fair and uniform, and that votes are fairly counted.
The organization Fair Vote has been pushing for a Right to Vote Amendment for a number of years. See, Fair Vote – Right to Vote Amendment.
In 2015 two Representatives introduces a Right to Vote Amendment, which states that:
SECTION 1. Every citizen of the United States, who is of legal voting age, shall have the fundamental right to vote in any public election held in the jurisdiction in which the citizen resides.
SECTION 2. Congress shall have the power to enforce and implement this article by appropriate legislation.
This is simple, reasonable, and fair. And it would prevent states from manipulating voting rules to disenfranchise voters.