Now that Donald Trump will be his party’s nominee, some Republicans have started saying that they would go Democrat or sit the race out. Mark Salter, a former top aide to Senator John McCain, tweeted: “The GOP is going to nominate for a President a guy who reads the National Inquirer and thinks it’s on the level. I’m with her.” Neither of the former president Bush is planning to endorse him at this time and former Republican presidential candidate Mitt Romney announced that he would not be attending the party convention this summer.

Clinton spokesman Brian Fallon said, “We have an informed understanding that we could have the potential to expect support from not just Democrats and independents, but Republicans too. There’s a time and place for that support to make itself known.” Trump is so unpredictable, so unconventional and, to some, so frightening that some conservative voters in red states would decide to cast their ballot for a Democrat who looks reasonable, experienced, and pretty center-of-the-road.

A clear precedent for this kind of campaign took place a little over 50 years ago. Going into the 1964 election, President Lyndon Johnson and his advisers were extremely concerned about how much the Civil Rights Act of 1964 would cost them in core Democratic states in the South. But the clouds started to clear for the incumbent when Republicans nominated Arizona Senator Barry Goldwater as their nominee. Goldwater was a right-wing conservative who adamantly defended conservatism in his convention speech. He attracted the kind of rough-and-tumble right-wing crowd that made many establishment Republicans squirm. He also had a penchant for making controversial statements.

In a conversation with his advisor Eddie Weisel over the summer, Johnson said that the Republican revolt against Goldwater would outweigh the Southern backlash against civil rights. Referring to himself in the third person, LBJ said: “Goldwater, among the Republicans, gets 50 percent. And Johnson gets 27. So the backlash to him is 27 percent, more than twice as much as the Democratic backlash. Yet you never read any columns or any editorials or anybody pointing up the Republican backlash… So you better say about the Republican backlash—all these extreme statements, and Ku Klux Klan, and all this other stuff.”

As the Democratic Convention approached, Johnson started to use the term “frontlash” to capture what he predicted would happen. He told advisor Dick Nelson, “call Bill Moyers and tell him to make copies of them and distribute them to all the networks. Try to get some of our people like [Texas Governor John] Connally and others to point out, then, what the polls show on the frontlash. Use nothing but the word frontlash; quit talking about the backlash.”

On the final day of the Democratic Convention in Atlantic City, Johnson spoke to Democratic leaders to inform them about his “frontlash” strategy and to urge them to spread the word. The goal was to bolster Democratic enthusiasm and to make a suggestion to Republicans who were leery about their frontrunner. Johnson cited opinion polls that showed Goldwater was receiving less support from Republican and Independent voters than Richard Nixon had in 1960. “We are finding that one out of every three Republicans stated they are part of the frontlash and will not vote Republican,” Johnson said. “We’ll gain two to three times as many as we lose.”

Johnson had ample reason to feel good about his prospects. National polls showed that he had a formidable lead over his opponent throughout the country. In the Republican state of Maine, support for Johnson over Goldwater was running seven to one. In Maryland, where Alabama Governor George Wallace had scared some Democrats by doing relatively well in the Democratic primaries with a campaign attacking civil rights, Johnson received 60 percent approval ratings. In Wisconsin, the other state where Wallace had done well, Johnson led Goldwater 53-25. Gallup reported in early September that Johnson was right about “frontlash.” More Republicans were planning to defect from their party than in any of the last seven presidential election cycles.

During the campaign, the Democratic National Committee made unprecedented use of television spots to convey the message that the president was a productive leader and Goldwater was a dangerous extremist “who would ruin this country and our future,” as Johnson aide Jack Valenti put it.

Johnson’s campaign team hired a first-rate advertising firm to handle his television spots. They released a blistering series of negative television ads designed to eviscerate Goldwater in the eyes of Democrats, independents, and nervous Republicans. The most famous of these ads went on the air on September 7, 1964. Viewers watch a little girl counting a daisy’s petals up to ten; then they hear a male voice counting down from ten to one. The camera zooms in on one of the girl’s eyes, and a nuclear explosion fills the screen. President Johnson, in voiceover, says: “These are the stakes—to make a world in which all of God’s children can live, or to go into the dark. We must either love each other, or we must die.” Another male voice says, “Vote for President Johnson on November 3. The stakes are too high for you to stay home.”

The Daisy Spot, though it aired only once, remains the most famous of the campaign. But there were other tough-minded ads that conveyed the notion that Goldwater’s domestic policy ideas were just as radical and dangerous as his foreign policy ideas. “Keep fear of Goldwater as unstable, impulsive, reckless in [the] public’s mind,” Valenti had advised Johnson. “This is our strongest asset.”

Johnson’s ad campaign specifically targeted Republicans who would not be comfortable with a Goldwater presidency. Central to their argument was not simply that Goldwater was a right-wing extremist but that he was unstable and could not be trusted with power. One of these showed a Republican voter, an actor, speaking to the camera, explaining why he was going to vote for a Democrat. In the four-minute ad, called “Confessions of a Republican,” a voter explains to viewers why he was not comfortable with his party’s nominee. “This man scares me,” he explained, especially since “weird groups” like the KKK had endorsed him.

The frontlash strategy worked. Johnson received endorsements from 60 of the 100 top newspapers (a stark contrast to the period between 1940 to 1960, when the top papers endorsed Republicans almost 77 percent of the time), including a number of major conservative publications such as the Hearst chain. Polls showed by late September that Johnson was trouncing Goldwater.

The election was a Democratic triumph. Johnson won 43,129,484 popular votes and 486 electoral votes to Goldwater’s 27,178,188 popular votes and 52 electoral votes. Johnson won the biggest popular vote, 61 percent, in American history, better than FDR in 1936, and registered the largest margin of victory. Goldwater’s extreme right-wing candidacy, as well as the excitement over Johnson’s legislation and the positive memories in the electorate of John Kennedy, drove the size of Democratic majorities to historic levels. The composition of Congress, which New York Times columnist James Reston would later term the “Goldwater Congress,” changed dramatically. With huge majorities in the House (295-140) and the Senate (68-23), Democrats would have more seats than at any time since 1938. The conservative coalition in Congress had been reduced to its smallest size since it had formed. The Senate Democratic majority was the biggest since 1940.

Democrats were disappointed that the Republicans carried the Deep South—Georgia, South Carolina, Alabama, Mississippi and Louisiana—though the Democratic South had started to crack before Goldwater came on the scene, and there were compensations to the Democrats for the loss of these states. African American voting, though still limited, increased and was almost entirely Democratic. Johnson had started to build a strong coalition in the coastal states and in the Republican Midwest, including in North Dakota, Missouri, Michigan, Iowa, Wisconsin, Minnesota and Iowa.

The “frontlash,” as Johnson had predicted, kept Republican voters away from the polls or impelled them to vote Democratic. Johnson won Kansas with 54.1 percent of the vote, the first time the state had not gone Republican since 1936. Maine went for the Democratic candidate for just the second time in the state’s history—and gave him 68 percent of the vote. Johnson also won in Vermont, which was ruby-red in those days and had not gone Democratic since the 1820s. Goldwater won only 16 non-Southern congressional districts. Democrats did extremely well among women, college educated voters, and the elderly, and in the big cities and the suburbs.

Today, a “frontlash” strategy would face obstacles that didn’t exist in 1964. Most important, the electorate is much more polarized than it was five decades ago. It is much more difficult, as a result of demographics, political institutions, and the media, to convince voters to flip from red to blue. And while many Republicans might not like Trump, they won’t be willing to go for a Democrat many of them regard as corrupt.

It also remains unclear whether the frontlash in 2016 will just be coming from the party elites rather than the voters. Given the anti-establishment sentiment in the electorate it is possible that Republican voters are more firmly entrenched in their support for their nominee this year than they were in 1964 even if leaders are backing away.

Yet Trump is such an outlier politically given his weak ties to the GOP and his unstable temperament, as well as his total lack of experience in politics, that the possibility does exist. If Hillary Clinton can recreate the frontlash strategy that Johnson used so successfully against Goldwater, she could be looking at a Democratic White House with a Democratic Congress with an opportunity to do the kind of big things her opponent Bernie Sanders has been talking about.