Why are congressional Republicans abandoning their nominee Donald Trump long after it was clear that he's manifestly unfit to hold any elected office, much less the presidency of the United States?

The simplest answer is usually the best. Here's my guess: Bigotry can be useful as long as it does not impact your core constituents. With video showing Trump admitting to the crime of sexual assault, and doing so in the foulest language possible, bigotry has come full circle for congressional Republicans. The bigotry that the GOP courted for decades to create a coalition large enough to capture the White House is now alienating a reliable voting bloc: middle-class white women.

Until last Friday, when the Washington Post reported on a video in which Trump claims his celebrity allows him to do anything he wants to women, including grabbing their genitalia, House and Senate Republicans felt insulated from his incendiary remarks. Voters who vowed never to support Trump could still be relied on for support, even if those Republicans endorsed Trump out of political expedience.

That is no longer the case. And that is something new.

Editorial Cartoons on Donald Trump View All 455 Images

It's well known that the Republican Party has pandered to the bigotry of reactionary politics since the 1960s when Richard Nixon, under the advisement of former Dixiecrat Strom Thurmond, invented with the help of advisers Roger Ailes and Kevin Phillips something called the Southern Strategy.

The Southern Strategy was a bundle of political messages and policy positions meant to appeal to segregationist Democrats alienated by their party's passage of the 1964 Civil Rights Act and 1965 Voting Rights Act. It started with Nixon's call for "law and order" in 1968. It was later used across the country.

Ronald Reagan's decrying of "welfare queens"; George H.W. Bush's "Willie Horton" attack ad; George W. Bush's spreading rumors that Arizona Sen. John McCain's adopted Bangladeshi daughter was an illegitimate black child; Newt Gingrich's claim in 2012 that Barack Obama is a "successful food stamp president" – all of these are a variation on the Southern Strategy theme.

A consequence of this has been the whitening of the Republican Party to such a degree that Trump's attacks on minorities and Muslims had no effect on actual Republicans. Conditions changed after the first debate when Clinton reminded everyone of Trump's fat-shaming of a teenaged beauty, but even then, the injury was to Trump alone, not on down-ticket Republicans.

But after the video emerged – which also showed Trump boasting of sexual advances toward a married woman who he later wanted fired from the Miss Universe contest due to her pregnancy – it was clear the support of middle-class white women was in jeopardy. That was enough for high-profile Republicans like McCain to rescind his endorsement. More telling, it was enough for House Republicans to follow suit, even calling for him to step down as the party's nominee.

Why telling? While it was clearer by the hour that Trump was losing, Republicans were optimistic about holding the Senate. And virtually no one doubted the party's hold of the House.

But now the House appears to be in play. Let's put it this way: Congressional Republicans are now damned if they do and damned if they don't. If they support Trump, they risk losing moderates (mostly middle-class white women). If they don't support Trump, they risk the ire of his core supporters.

This is why we are seeing leaders like House Speaker Paul Ryan turn themselves into pretzels. On Monday, he said he would no longer campaign for or defend Trump, but at the same time, he did not withdraw his endorsement. His announcement suggests he knows Trump is doomed, that his base is a significant threat and that he must protect House Republicans from both.

This context is enough for Sean Trende, a sober analyst at RealClearPolitics, to argue that while Democrats are not favored the win the House, the prospect must now be taken seriously.

Editorial Cartoons on the 2016 Presidential Elections View All 596 Images

All of this has revived the notion of civil war within the Republican Party and the possibility of a party split. That split, I contend, will be led by GOP elites if it happens at all, and that decision will be determined by the answer to this question: To what degree does bigotry remain a useful political tool?

If appeals to bigotry still have utility, as they have in forming past coalitions large enough to capture the White House, then I'd say a split, while not impossible, is extremely unlikely. But if it is determined that bigotry is actually harming not just Republican national ambitions but the trusted support of core constituents of the party itself, I'd say a split is entirely possible.