Presidents are determined by the electoral college. We know this. But there are many reasons why this does matter, some good, some not good at all. David Wasserman of The Cook Political Report and 538 is my favorite election numbers counter at this point. Last night on Twitter he noted that in the last four House elections, Republicans have consistently won 4% more seats than votes in the last three House elections.
2012: 49% of 2-party vote, 53% of seats 2014: 53% of vote, 57% of seats 2016: 51% of vote, 55% of seats
Needless to say, that consistency isn't happenstance. It's structural.
A significant amount of this is due to the GOP's extremely effective 2010 gerrymandering. But it's not just that and probably not mostly that. Democrats are geographically concentrated in ways that hurt them in federal elections. This is one reason it is absolutely critical for Democrats to focus on state legislatures and governorships in 2018 and 2020. Geographical concentration creates inherent problems in our system. When you add the exacerbating effect of gerrymandering you can get close to a lock in a still roughly evenly divided polity.