Because The 55 Republicans Senators represent states with a population of 112,858,577 residents or 49%, while the 45 Democratic and Independent Senators represent States with a total of 117,657,044 residents or 51% of the population.
Thus Common Sense Mom @ Daily Kos explains:
We all understand that the Senate was set up as a "check and balance" to the inherently more politically populace driven House of Representatives. By choosing Senators by State instead of population, the founding fathers hoped to protect the rights of the minority against the "tyranny of the majority." But if population is considered, or the vote count received by each Senator, there is no doubt that our founding fathers' fear is being turned on its head.
Republican Senators, in fact, represent a minority of Americans. If the "nuclear option" is utilized to strip Democratic Senators, who represent more Americans, of their right to dissent, then we will have a TYRANNY OF THE MINORITY!
Thomas Jefferson must be rolling in his grave.
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