The Constitution guarantees it.
Eric Black | Columnist for MINNPost
“But, according to the calculation of Ian Millhiser, writing for Vox, if you add up the population of states and assign half to each of their two senators, “the Democratic half of the Senate represents 41,549,808 more people (12.5%) than the Republican half.”
“Millhiser’s piece is named after that fact: “America’s anti-democratic Senate, in one number.”
“In the very short Article V, which lays out the process for amending the Constitution (you know: two-thirds of both houses have to agree and then three-quarters of all the states have to ratify) there is one provision of the Constitution that the Constitution itself says can never be changed. It says, clearly and bluntly: “that no State, without its Consent, shall be deprived of its equal Suffrage in the Senate.””