Recent polls contain a finding that is devastating to Donald Trump’s presidential candidacy: He is losing the Catholic vote to Hillary Clinton by an astounding 23 percentage points. However, Trump retains the sort of support from white evangelical Protestants that is typical of recent Republican presidential nominees – around 80 percent.

This contrast doesn’t just matter for Trump’s candidacy. It reveals a startling political splintering of conservative Catholics and evangelicals, who have tracked side by side for decades.

This alliance of Catholics and evangelicals came about in the 1970s. Before that, Catholics were a solid Democratic Party voting bloc, comprised largely of the immigrant underclass. Economic and social status, not moral issues, determined Catholic voting.

In the 1970s, social issues drove many Catholics to question their steadfast loyalty to the Democratic Party. By the 1980s, many were voting Republican, due not only to social issues but also to their own improved economic and social status. Evangelical-led organizations, such as the Christian Coalition, in the 1990s made Catholic outreach a priority in their efforts at building support.

Throughout the long years of partnership, Catholics have continued to hold less conservative positions than white evangelicals on many issues: immigration, the death penalty, health care, social welfare and more.

Trump has pushed a lot of these Catholics over the edge, especially with his strident immigration stands. Issues surrounding Trump’s personal conduct also have turned away some leading conservative Catholics. Dozens of conservative Catholic thought leaders signed a letter that declared Trump “manifestly unfit to be President of the United States” and said that he does not represent Catholic values.

But white evangelical voters are standing firm for Trump. That is a significant contrast with the many normally Republican-voting Catholics opposing Trump.

For four decades, political and religious leaders worked hard to bring together evangelical and Catholic voters on key moral issues. They achieved for some time a truly powerful alliance. The Trump candidacy now threatens to pull these groups back away from each other.