Can they really? The popular vote isn't enough to win a presidential election, you also need electoral college votes which aren't allocated by proportion of population.
At the local and state level, you can strategically implement gerrymandering to create electoral districts that are strongly advantageous to you. How would a political challenger not belonging to the dominant party win there?
Authoritarian regimes frequently win elections with 80-95% of the vote. That tells me that the people "can" vote him out.
