A better comparison isn't to "votes cast", but to "theoretical voting population". 2020 saw a massive jump in voter turnout, too; from 54.8% in 2016 to 62% in 2020, the only election since 1936 with a higher turnout was 1960;
https://en.wikipedia.org/wiki/Voter_...tial_elections
If we use the voting-age population from that same page, 74.2m for Trump was 28.8% of the voter base.
Romney's 60.9m was 25.6%.
Bush's best year was 2004 rather than the tight contest with Gore; he got 62.0m, so 28.2% of the total voting-age population that year.
Still short of Trump in 2020.
Seriously, Trump is one of the most
wildly popular Republican Presidents in history. Yes, he's an enormous unfunny clown, but don't let that make you overlook the
data. There, we've accounted for population growth,
and for overall voter turnout. Trump's the best the Republicans have done since Reagan in '84, in terms of turnout. And Reagan took
every State but Minnesota and DC.