Big difference is that Republicans have the electoral college in their favor. Democrats have to work harder to win. So many red states with fewer people than a blue state city.
Oh, sure. The current GOP edge in the EC is real (it wasn't always!) but it's not all THAT big. A couple points. And Trump's not gonna win the popular vote, lol. So it's a tight path to victory but absolutely doable no matter WHO the candidate is four months from now.