Math has a liberal bias

[Anymouse]

The history of this country has shown that the electorate has always been fickle, and the party in power is subject to the electorate...the left may have the majority now, but that's always subject to change from one election to the next.

I am not sure I would call the Democrats "the Left." I think a more accurate representation of the Democrats are "the slightly less Right."
And as for the Dems having the majority, they do not, at least in the House.
Moreover, because of the way electoral votes are apportioned (one for each representative and one for each senator), the red states (GOP) get additional electoral votes (because there are more red states). The blue states (those with the majority of the population) do not get as many electoral votes for senators (because there are less states, though they have more people).
As the system is currently set up, the GOP red states therefore have an advantage going in (assuming no states flip parties) because there are more of them. Not more people or votes, just more (sparsely populated) states (like mine). The GOP can occasionally afford to lose a red state (because there are so many red states), while the Dems cannot afford to lose blue states (because there are so many people).