These numbers point to one undeniable conclusion: white Protestant Christians—both mainline and evangelical—are aging and quickly losing ground as a proportion of the population.

While these transformations are most pronounced in the general population, they can also be seen—albeit in a delayed fashion—among voters in national elections.

The stair-step downward trajectory of white Christian presence in the electorate over the last three decades is stunningly clear. In 1992, when Bill Clinton was elected to his first term as president, nearly three quarters of the electorate was white and Christian. By 2012, white Christians’ influence had declined precipitously, comprising only 57 percent of the electorate. A linear forecast line based on these trends demonstrates that what might be called a “white Christian strategy”—relying on supermajorities of white Christian votes to offset demographic changes—will yield diminishing returns in each successive national election cycle. White Christians will likely make up 55 percent of voters in 2016 and drop to 52 percent of voters by the following presidential campaign in 2020. If current trends hold steady, 2024 will be a watershed year—the first American election in which white Christians do not constitute a majority of voters.

The chart demonstrates that every midterm election, the GOP essentially gets to rewind the clock. Low turnout among young and minority voters allows the GOP to carry over whatever advantage they had in the last presidential election among white Christian voters into the following midterm election. But even this “midterm time warp” GOP advantage is fading over time. Newt Gingrich’s 1994 revolution relied on an electorate that was 74 percent white and Christian. The more recent Tea Party wave of 2010 banked on an electorate in which 61 percent of voters were white and Christian. And the 2014 Republican gains leveraged an electorate that was only 58 percent white and Christian.

For GOP leaders, the reliably Republican midterm constituency may seem like a bonus—a chance for the party to make up ground and reinforce their connection with their base. But in other important ways, it’s a distraction that undermines the GOP’s long-term goal of creating a more diverse electoral coalition. In this light, it’s easy to see why the Republicans refused to pass immigration reform or loosen their rhetoric on gay rights with a year to go before the midterms.

These actions could have created havoc among their most reliable supporters. But it’s clear that these appeals to white Christians, while helpful in some short-term fights, sealed the fate of the Romney campaign in 2012 and will likely set the GOP back as it turns to the task of reclaiming the White House in 2016.

The numbers demonstrate the shortsightedness of the GOP’s continued reliance on the white Christian strategy in this climate. As data from the National Exit Polls demonstrate, in 1992 the voting coalitions of both George H.W. Bush and Bill Clinton were mostly white and Christian. President Bush received 86 percent of his support from white Christians, while Clinton’s total was 60 percent. This spread remained steady through both Clinton elections in the 1990s, but the religious composition of partisan voting coalitions subsequently began to drift apart in the 2000s. Even as the proportion of white Christian voters in the electorate dropped from 73 percent in 1992 to 57 percent in 2012, Republican Party candidates including Romney have continued to rely on voting coalitions in which approximately eight out of every 10 supporters are white and Christian. Democratic candidates, by contrast, have more closely followed the changing demographics in the country. Whereas Bill Clinton’s winning coalition in 1992 was 60 percent white Christian, Obama’s winning coalition in 2012 was only 37 percent white Christian. The result is that the white Christian strategy has left Republicans dependent on a steadily shrinking slice of the electorate.