If you are still struggling to understand why evangelical Christians so heartily embrace President Trump — perhaps the closest thing in American life to a walking, breathing personification of the seven deadly sins — the answer came this weekend with his utterly unsurprising nomination of Amy Coney Barrett to the Supreme Court.

The math here is simple: Trump has reason to believe he owes his 2016 election, in part, to overwhelming support from white evangelicals. He hopes they'll help carry him across the finish line again in 2020. For more than a generation, the No. 1 evangelical political goal has been to overturn Roe v. Wade, the 1973 court ruling that the Constitution protects a woman's right to have an abortion. And Barrett seems almost certain to supply that vote.

Trump is working to retain the loyalty of conservative Christians, in other words, by openly and happily giving them what they want to a degree matched by no other president. Trump is often described as transactional. Well, so are his voters. Trump's personal life matters much less to them than how he governs.

"I can say, without question, that Donald Trump has probably been the most pro-life [president] we've ever had," said Rick Santorum, the socially conservative former GOP senator from Pennsylvania.

That is probably true. GOP presidents going back to Ronald Reagan have all paid lip-service to the pro-life cause, and have routinely imposed a "global gag order" that prohibits U.S. funding of international organizations that provide abortion counseling or referrals. Closer to home, though, their commitment could seem more calculated and less certain — they never showed up in-person to the annual "March for Life," as though they didn't want to be seen with pro-life activists. And when it came to appointing Supreme Court justices, Republican presidents provided a long list of disappointments for the cause: Sandra Day O'Connor. David Souter. Anthony Kennedy.

This contributed to what might be called the What's the Matter with Kansas? problem for anti-abortion activists. That Thomas Frank book posited that working class conservatives voted for Republicans against their own economic interests — and that they did so because GOP candidates talked a lot about culture war issues like abortion, but focused their real energies on cutting taxes and weakening the safety net once in office. In this analysis, the GOP's fusion between economic conservatives and social conservatives was built on lies and distractions.

It's not clear the issue ever really threatened the conservative coalition: Evangelicals gave substantial support to GOP candidates George W. Bush, John McCain and Mitt Romney. McCain and Romney lost, of course, but Bush won his first term in 2000 — losing the popular vote, but winning the Electoral College — in part by clinching an outsized portion, even for Republicans, of the evangelical vote. And he won re-election in 2004 with a strategy that focused even more on getting evangelicals to the polls: That was the year Karl Rove helped put anti-gay marriage initiatives on the ballot in many swing states.

Bush had an advantage among evangelicals and other conservative Christians, though: He was one of them. Trump obviously isn't. So to duplicate Bush's winning strategy, Trump said out loud the thing previous GOP presidents had mostly hinted at: He promised to appoint pro-life judges, dispensing with usual euphemisms about "constitutional conservatism" used by his predecessors. It worked. In 2016, Trump got the highest proportion of evangelical votes since Bush's 2004 effort.

He has stuck with the strategy. When Chief Justice John Roberts — a Bush appointee — disappointed conservatives on a key abortion vote earlier this year, Trump promised to double down on the effort. With Barrett's nomination, he is making good on that process.

That might seem foolish, on one level: A recent NPR/Marist poll showed that 56 percent of registered voters describe themselves as "pro-choice" — and just 36 percent describe themselves as "pro-life." But that same poll also revealed that just 8 percent of pro-choice voters said the abortion issue was the most important factor in determining their vote, while 17 percent of pro-life voters said the same. What anti-abortion voters lack in numbers, they make up for in intensity. (That dynamic could flip, though, if Roe v. Wade is overturned.)

Trump, of course, has never been the kind of candidate to pivot to the middle in order to attract votes. He's all about that base. There are signs, though, that the president's appeal is slipping — at least one poll has revealed that "Trump is poised to lose a sizable chunk of his Christian voters" in November. So his campaign is looking to do what it can to shore up its support among those usually reliable voters — which explains the GOP's recent efforts to cast former Vice President Joe Biden and Democrats as anti-religious.

There has been much speculation, fed by Trump himself, that Republicans want Barrett on the court by November in order to cast a deciding vote if (as happened with Bush v. Gore in 2000) the election is thrown to the courts. It is just as likely, though, that Trump is using the nomination as a get-out-the-vote effort. Barrett won't just save Trump's campaign — right now, she is the campaign.

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