In the United States, Southern Democrats reacted in a similar manner to the Reconstruction-era enfranchisement of African-Americans. Mandated by the 15th Amendment, which was ratified in 1870, black suffrage not only imperiled Southern Democrats’ political dominance but also challenged longstanding patterns of white supremacy. Since African-Americans represented a majority or near majority in many of the post-Confederate states, Southern Democrats viewed their enfranchisement as an existential threat. So they, too, played dirty.

Between 1885 and 1908, all 11 post-Confederate states passed laws establishing poll taxes, literacy tests, property and residency requirements and other measures aimed at stripping African-Americans of their voting rights — and locking in Democratic Party dominance. In Tennessee, where the 1889 Dortch Law would disenfranchise illiterate black voters, one newspaper editorialized, “Give us the Dortch bill or we perish.” These measures, building on a monstrous campaign of anti-black violence, did precisely what they were intended to do: Black turnout in the South fell to 2 percent in 1912 from 61 percent in 1880. Unwilling to lose, Southern Democrats stripped the right to vote from millions of people, ushering in nearly a century of authoritarian rule in the South.

Republicans appear to be in the grip of a similar panic today. Their medium-term electoral prospects are dim. For one, they remain an overwhelmingly white Christian party in an increasingly diverse society. As a share of the American electorate, white Christians declined from 73 percent in 1992 to 57 percent in 2012 and may be below 50 percent by 2024. Republicans also face a generational challenge: Younger voters are deserting them. In 2018, 18- to 29-year-olds voted for Democrats by more than 2 to 1, and 30-somethings voted nearly 60 percent for Democrats.

Demography is not destiny, but as California Republicans have discovered, it often punishes parties that fail to adapt to changing societies. The growing diversity of the American electorate is making it harder for the Republican Party to win national majorities. Republicans have won the popular vote in presidential elections just once in the last 30 years. Donald Trump captured this Republican pessimism well when he told the Christian Broadcasting Network in 2016, “I think this is the last election the Republicans have a chance of winning because you are going to have people flowing across the border.”

“If we don’t win this election,” Mr. Trump added, “you’ll never see another Republican.”

The problem runs deeper than electoral math, however. Much of the Republican base views defeat as catastrophic. White Christians are losing more than an electoral majority; their once-dominant status in American society is eroding. Half a century ago, white Protestant men occupied nearly all our country’s high-status positions: They made up nearly all the elected officials, business leaders and media figures. Those days are over, but the loss of a group’s social status can feel deeply threatening. Many rank-and-file Republicans believe that the country they grew up in is being taken away from them. Slogans like “take our country back” and “make America great again” reflect this sense of peril.

So like the old Southern Democrats, modern-day Republicans have responded to darkening electoral horizons and rank-and-file perceptions of existential threat with a win-at-any-cost mentality. Most reminiscent of the Jim Crow South are Republican efforts to tilt the electoral playing field. Since 2010, a dozen Republican-led states have adopted new laws making it more difficult to register or vote. Republican state and local governments have closed polling places in predominantly African-American neighborhoods, purged voter rolls and created new obstacles to registration and voting.

In Georgia, a 2017 “exact match law” allowed authorities to throw out voter registration forms whose information did not “exactly match” existing records. Brian Kemp, who was simultaneously Georgia’s secretary of state and the 2018 Republican candidate for governor, tried to use the law to invalidate tens of thousands of registration forms, many of which were from African-Americans. In Tennessee, Republicans recently passed chilling legislation allowing criminal charges to be levied against voter registration groups that submit incomplete forms or miss deadlines. And in Texas this year, Republicans attempted to purge the voter rolls of nearly 100,000 Latinos.