Brennan Linsley / AP

This week’s cascade of Republican defections from Donald Trump has plunged the GOP into the deepest general-election divide over its presidential nominee in more than 50 years.

The apex of modern GOP general-election conflict came in 1964 when Barry Goldwater, as the tribune of an emerging Sunbelt- and suburbia-based conservative movement, captured the nomination over resistance from the party’s previously dominant Eastern establishment. But the Republican contortions over Trump are surpassing even the fratricide over Goldwater. The dissent crested this week with a letter from 50 GOP former national security officials denouncing him; Senator Susan Collins of Maine’s declaration that she would not support him; and Wednesday’s launch of a committee of dozens of GOP luminaries, including three former Cabinet officers and six current or former House members who endorsed Hillary Clinton.

Whether or not Trump can catch Clinton by November, the greatest question facing Republicans may be whether these fractures over their blustery nominee will trigger a lasting power shift in the party—just as the divides over Goldwater did, despite his resounding loss to Lyndon Johnson.

From 1940 through 1960, the GOP’s loosely defined establishment—globalist in foreign affairs, moderate on domestic issues, and centered in Wall Street and the Fortune 500—had reliably picked the nominee. But when Goldwater emerged, championing a more confrontational conservatism rooted in the South and Southwest, that establishment proved ineffective at stopping him, just like today’s party leaders who are dubious of Trump. Party centrists rallied behind a procession of alternatives—Henry Cabot Lodge, Nelson Rockefeller, and finally William Scranton, a particular favorite of GOP governors—all to little effect.

The historian Geoffrey Kabaservice, the author of Rule and Ruin, a history of moderate Republicans, says the GOP center didn’t feel true urgency about stopping Goldwater until he voted to oppose the landmark Civil Rights Act in June 1964. Like Trump’s critics today, Goldwater’s skeptics worried he was dangerously redefining the GOP as a party of racial backlash. “In a lot of ways it was a fight against Goldwater’s Southern strategy,” Kabaservice said. Scranton belatedly entered the race one day after Goldwater’s vote, hoping to block him at the convention. But he was too late.

Once Goldwater was nominated, elected officials undertook gyrations Paul Ryan and Mitch McConnell would recognize today. Candidates often discovered pressing business elsewhere when Goldwater visited their state. Yet very few formally broke from the nominee—almost all who did were in the Northeast. However ambivalently, Scranton and even Rockefeller endorsed the nominee, the latter even after his feral heckling from Goldwater partisans at the convention. Despite his private doubts, former President Dwight Eisenhower, after an August party-unity conference, expressed his “full support for the Republican national ticket” and cut a television testimonial for Goldwater. Richard Nixon, the once and future nominee, actively campaigned for him. “You didn’t have the party leadership abandoning their nominee,” said Jonathan Darman, the author of Landslide, a recent book on the 1964 election. “They weren't saying, ‘we can't support this guy, he's outside of the mainstream.’”

With multiple Republican House members, GOP senators from six states, and at least four GOP governors all withholding their support, Trump is already facing more defection from current elected officials than Goldwater did. And, compared to Goldwater’s relations with Eisenhower, Nixon, and even Thomas Dewey, who was most skeptical of him, Trump is much more estranged from most other recent GOP presidential nominees. That separation ranges from open opposition from Mitt Romney to pointed silence from George Bush elder and younger to chilly detente with John McCain.

Another contrast is the concentrated opposition to Trump from the GOP’s national-security leadership. Several former Eisenhower Cabinet officials endorsed Johnson in 1964, but they came primarily from domestic posts. The “National Independent Committee” for Johnson—organized by Robert Anderson, Eisenhower’s treasury secretary and preferred successor—revolved primarily around business leaders like Henry Ford II. This week’s letter from former GOP national-security officials declaring that Trump “lacks the character, values and experience to be president” represents a much sharper attack on the nominee’s fitness than any defecting group leveled against Goldwater.

In 1964, the GOP’s deep fissures contributed to Johnson’s crushing victory. But ultimately the forces of Northeastern moderation that resisted Goldwater lost control of the party to the Sunbelt conservatives that elevated him. Ronald Reagan, softening some key elements, followed a Goldwater-like ideological and geographic path to victory 16 years later—but at the price of defining the GOP in ways that eventually alienated the Northeastern and West Coast states most skeptical of that agenda. Goldwater’s “Southern strategy” of courting white Dixie conservatives, later reinforced by Nixon and Reagan, also lastingly alienated African Americans.

The story is similar for the modern Democratic nominee who most divided his party: George McGovern in 1972. McGovern prefigured a culturally liberal Democratic coalition that would mobilize young people, minorities, and white professionals—the coalition that, decades later, twice elected President Obama. But the widespread defections McGovern faced in his landslide defeat by Nixon—when the AFL-CIO refused to endorse him and former Texas Governor John Connally led a robust Democrats for Nixon organization—also foreshadowed his party’s later retreat among the white working-class and in the South.

The GOP’s Trump divide could herald another reconfiguration. Like Goldwater and McGovern, Trump represents a breakthrough victory for a rising party faction, in his case working-class whites drawn to his racially barbed nationalism. And like those predecessors, Trump could also precipitate historic losses among voters his party had previously relied upon, like college-educated whites, or hoped to add, like Hispanics and other minorities. If Goldwater and McGovern are any guide, the aftershocks of Trump’s insurrection will rattle and reshape the GOP long after November—win or lose.

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