Trump is the first GOP Presidential nominee to get 76 million votes. Guess Eisenhower, Nixon, Reagan are jealous LOL.
. . . Why would they be? Eisenhower had 35.5 million in his largest election, out of a population of 164 million, meaning he got 21.6% of Americans voting for him and 57.4% of the popular vote cast. Nixon in his biggest victory got ~41 million out of a population of 205 million, so 20% of the population and 60.7% of the total votes cast. Reagan got 54.5 million out of a population of 233 million, so 23% of the population and 58.8% of votes cast.
Meanwhile Trump's 76 million is out of a population of 342 million, so 22% of the population and 50.1% of votes cast.
In other words, Trump got about the same percent of the population voting for him as other popular Republican presidents, with Reagan pulling the largest percentage wise while Nixon managed the largest percent of votes cast, which Trump lags behind considerably compared to the others.
Every Republican President has generally gotten more votes in total than the prior winner... since, yanno, the population of the US has been consistently going up. This might change in the future but for all the cited Presidents it's been the trend.
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Edit: Before folks jump to conclusions about how this is such a low percentage of the population, remember that the total population includes children, which account for anywhere from a quarter to a third of the population depending on the year (lower percentage as we get more modern), as well as those who have lost the right to vote, illegal and legal immigrants, those that choose not to vote, etc.