There are several ways that our system gives less voting power to one group of people than another. Redistricting, while improving, is still used as a political tool to hurt your opponent and, even when not, is nearly impossible to do fairly. The Senate ensures that voters in states with small population have far more influence than those with a large population. Since the Electoral College is based on seats in Congress, the advantage in the Senate gives small states greater influence when choosing the presidency.
The gulf in population size between large and small states has grown worse in recent decades, a trend that will only continue. This explains how the popular vote loser has won in two of the last five presidential elections and points towards the likelihood of it continuing to happen.