One of the more curious aspects of American democracy is that it is literally unconstitutional for states to adopt the same system of government as the nation as a whole. In the case of Reynolds v. Sims in 1964, the Supreme Court ruled that all state legislature districts have to have roughly equal populations, because the Equal Protection Clause of the 14th Amendment enshrines a principle of “one man, one vote.” That means that an institution like the US Senate, with wildly unequal populations in its various “districts,” cannot exist at the state level — at least not anymore.The rapid changes Reynolds imposed on the structure of many state governments gives us an interesting opportunity to study what kinds of changes we might expect were the US Senate ever to be replaced with a more representative institution (or abolished outright). The evidence suggests that the malapportionment of the Senate is, in fact, a big deal that probably leads the federal government to spend substantially more in places like Wyoming and Vermont and substantially less in places like California and Texas than would otherwise be the case.

Source: The Senate is so crazily designed it would be literally illegal for a US state to copy it – Vox