US population is 329 million.
US adult over 18 is 253,768,092
80 million is 31%.
On average presidential voter turnout is roughly 56.7% or 143,886,508.
80 million is 55%.
The 36-year average voter turnout rate for presidential election years between 1980 and 2016 was 56.7%. The lowest recorded voter turnout rate was in 1996 when little more than half of eligible voters took to the polls, 51.7%. In the 2016 election, the rate was 60.1%.