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.