A year ago, the late Andrew Kohut examined how the Democratic Party has drifted to the left in recent years. In some ways, this is a departure (as on support for gay marriage) and in some ways it is a return (“liberal self-identification has edged up to its highest level in more than 20 years”). It has been hard to miss the signs. The centrist Democratic Leadership Council became so marginalized and irrelevant during the Iraq War years that it went out of business. The Blue Dog caucus in Congress has been utterly decimated since Obama was sworn into office in 2009. Joe Lieberman, the party’s vice-presidential candidate in 2000, was defeated in a primary and finished his career as an independent.

But, a party takes a long time to completely lose its DNA. You can date the modern Democratic Party to the election of FDR in 1932. For the first thirty-plus years of its modern existence, it co-existed as the party of the anti-Catholic Jim Crow south and the very Catholic and racially diverse northern urban machines and union movements. Even today, Democrats are more at ease than Republicans with making odd coalitions of convenience and settling for less than ideal compromises. Part of the reason for this, though, is that the Democrats controlled Congress almost uninterrupted for the first sixty-two years of their post-1932 existence. They had the responsibility to govern so they learned the techniques of governance.

The Republican Party’s DNA is different. They spent those first 62 years largely in the Congressional wilderness. They were siloed in the north and in the suburbs, and in the southwest and left coast. When they had power it was in the White House, and their presidents (including Reagan) had to, for the most part, deal with Democrats in Congress. Because the rank-and-file didn’t have to take responsibility for legislating, and because they didn’t like most of the legislation that was created, they developed a permanent minority, anti-federal government mentality. They also developed the tools and habits that make a minority party successful.

These characteristics have proven to be very resilient despite the 1994 Gingrich Revolution that brought Republican dominance to Congress, and despite the eight-year run of the Bush administration.

One area where Republicans have been able to fuse disparate elements is in the anti-choice movement, where conservative Catholics and evangelical protestants have made alliance over the forty-three years since the Roe v. Wade decision. We saw the fissure line there open up a bit last week in South Carolina when the Republican frontrunner and Pope Francis got into a fight over immigration policy.

The death of Antonin Scalia and the impending fight over his replacement are interesting in this context. Justice Scalia was the greatest living symbol of this fusion between the Moral Majority of Jerry Falwell and conservative Catholicism. Scalia was also the leading voice (post-Reagan) and most powerful player in the Conservative Movement’s long war against the FDR coalition’s legacy and accomplishments.

It’s not an accident that this symbiotic relationship developed during Pope John Paul II’s time in the Vatican and that it is on less solid footing during the papacy of the more liberal-minded Pope Francis.

These tensions should be kept in mind when thinking about what’s going on in the Republican primaries. The original victims of anti-immigration nativist politics were the Catholic immigrants of the mid-19th Century. The Know-Nothings and similar-minded anti-Catholic Whigs were merged into the abolitionist elements of the Republican Party from the very beginning. Call it the Jim Crow of the north.

Some of that DNA is left over, both in the nativist impulses of the right and the less hostile attitude of modern Catholics, including Republican Catholics.

There’s a big difference between how John Kasich (a lapsed-Catholic Anglican) and Jeb Bush (a Catholic convert) feel about Latino immigrants and how Donald Trump and most of his supporters feel about them.

And that helps explain why Trump has more appeal with evangelicals despite being a man of low morals and no apparent faith.

The very idea that Trump will encounter resistance outside the South is based on a simplistic and doubly inapt conception of “moderation.” The first premise is that, by promising to appeal outside of the Republican Party’s typical constituencies, Rubio is by definition more moderate than Trump; the second is that appealing to the center in a general election is no different than appealing to “moderate” Republicans in a GOP primary.

If this race is proving anything, though, it’s that what constitutes “moderation” to elite conservatives (relative dovishness on immigration aimed at swing voters in a general election) isn’t what constitutes moderation among Republican voters (restrictionist immigration policy paired with heterodox support for redistributive social policies). The big flaw in the assumption that Rubio (or anyone, really) can make up ground against Trump in blue states is that “moderate” voters are actually Trump’s ace in the hole.

As a (very) general matter, Catholics are more supportive of redistributive social policies than evangelicals. Look no further than the pope for proof of this, but it’s also why so many white Catholics in Congress are Democrats. Al Smith was a Democrat. JFK was a Democrat. Joe Biden is a Democrat.

But even evangelicals are more supportive of social spending than the libertarians and Wall Street elite. They aren’t free trade absolutists and they’re not clamoring to destroy Social Security and Medicare.

What Trump seems to be doing is winning over the evangelicals with his hardline on immigration without alienating them with his heresies against Ayn Rand Republicanism. And he’s muddling his message enough on social issues to seem moderate compared to his opponents.

It’s a sweet spot.

But it’s a sweet spot that’s sitting on some active fault lines.

His success is going to put the Republican Party as we’ve known it through some threshing blades. What comes out the other side is going to be a shredded mess.