Technically, the U.S. Constitution doesn't guarantee the right to vote. It seems odd, considering all of the various other rights, guarantees and structural details enumerated in the document, but it doesn't.

That said, there are amendments that provide reasons why certain groups of people can't be denied suffrage. In other words, there's nothing that says, "All Americans have the right to vote." Yet there are passages that say, Americans can't be denied the right to vote because of [race, gender, etc...]