The left argument simply assumes that the “popular vote” in the aggregate nationally is, or at least ought to be, the standard by which the presidential election is judged to be legitimate; anything else is illegitimate and “unrepresentative”, and the Senate inherently so. But there was never any intention to have “one man, one vote” be the appropriate standard of legitimacy on the national level as it was at more local levels. The founders wanted to force a widespread consensus across a whole collection of local majorities to balance different interests. This prevents ten or a dozen urban aggregations (NY, LA, SF, Chicago…) from dominating without having to balance other interests. The “popular vote” in the aggregate nationally is just a journalistic construct that is entirely extra-constitutional.