I posted this answer:
For as long as I can remember -- and that’s a long time -- so-called conventional wisdom has held that high voter turnout is bad for Republicans. It turns out, the evidence refutes that myth. The 2020 election exploded that conventional wisdom convincingly.
As the New York Times’s David Leonard reported on 12/23/21, On the Myth that High Turnout Benefits Dems,
In 2020, turnout soared, yet Democrats did worse than expected. Yes, they defeated Trump, but they failed to retake the Senate (for now) and lost ground in the House and in state legislatures.*
The Associated Press made the point that lower turnout may even hurt the Republicans as much as, or more than, the Democrats, noting:
In Iowa, 76% of eligible voters cast ballots last November, among the highest rates in the nation, as Republicans swept races up and down the ballot. Trump easily won the state in what had been expected to be a close race, Republican Joni Ernst won reelection to the U.S. Senate, and Republicans flipped two U.S. House seats with no major problems or fraud reported.
In an article for Commentary, Republicans, Stop Believing Your Own Election Myth, Chris Stirewalt observes that high turnout does not favor Democrats, and provides several examples to back up the claim:
Both sides attribute President Biden’s victory to this increased turnout, but this is probably false. In their book The Turnout Myth, political scientists Daron Shaw and John Petrocik put to rest the old saws about the subject. In 2006, Democrats swept in a low-turnout vote, but they got crushed in the midterms four years later when turnout increased dramatically. Turnout climbed from 2000 to 2004—but Republicans performed better at every level. Like those cycles, 2020 offered no evidence that bigger is bluer. Even as Biden was winning, Republicans defied expectations, gaining House seats and keeping a lock on statehouses across the country. It was not a blue wave that swept Trump from office. Rather, it was the nudge from moderate voters in the suburbs of big cities in swing states. Nor was it mail-in voting that made the difference. A study from Stanford’s Institute for Economic Policy research presents very strong evidence that mail-in voting itself did not drive the turnout surge, nor did it constitute any significant partisan advantage.
Jon Ward makes the same point for Yahoo News, adding:
And this gets to the second major implication of the turnout myth: Republican fears [that] a more diverse country [favors Democrats] appear to have been largely unfounded.
The 2020 election was a perfect example of this. The GOP lost the presidency but won most of the competitive U.S. Senate races and gained seats in the House. It also did much better in state legislative races than expected.
And while we’re at it, let’s take a look at another myth that got tarnished in 2020 -- that the Democrats have a lock on the urban vote. As The Washington Post reported, Trump wasn’t just a rural phenomenon. Most of his supporters come from cities and suburbs:
Folks who talk about President Trump’s rural base are missing something.
Are rural Americans Trump voters? Yes, many of them. Trump voters outnumber voters who supported Joe Biden 2 to 1 in rural counties.
But are all Trump voters rural? Absolutely not. Voters in rural America accounted for less than a fifth of all votes cast for him.
Biden won a bit more than half of the urban vote, but it wasn’t a blowout victory — Trump had urban majorities in 21 states.
For the record, I do not have a political ax to grind here. I am an Independent not just as a registered voter but also philosophically.
* The Democrats eventually won two Georgia’s two senate seats in a January runoff, giving them a tie in the Senate and effective control. But I believe it highly likely that Donald Trump’s voter fraud conspiracy rantings against Georgia’s election process discouraged enough GOP voters from voting that he swung that election to the Democrats.