In her new book, Why I Lost, 2016 Democratic presidential nominee Hillary Clinton puts some of the blame for her general election loss to Republican Donald Trump on her primary opponent, Bernie Sanders. Clinton writes:

His attacks caused lasting damage, making it harder to unify progressives in the general election and paving the way for Trump’s “Crooked Hillary” campaign.

Like 2008, many in the Democratic establishment assumed the primary would be a coronation for Clinton. When Sanders announced his candidacy, it was with little fanfare. The political intelligencia viewed the Vermont Democratic Socialist as a gadfly who would barely register support.

To Hillary’s chagrin, Sanders’ campaign became a movement. There was a vacuum, which he filled. Many in the Democratic Party felt that they had held their nose and supported candidates in the past who were too close to what Sanders terms “large financial institutions.” There was also an anti-foreign interventionist strand in the party, which was disaffected by the hawkish policies supported by Clinton, including her support for a troop surge in Afghanistan, an invasion of Libya, and her support for Israel during its 2014 military campaign in Gaza.

No other candidate filled that vacuum like Sanders. He became a tribune for voters who had lost faith in the political establishment. By Sanders becoming the voice of the disaffected left, Clinton became styled as a voice of the establishment. This made the primary a lot more competitive than most expected and cast Clinton as the candidate of the big financial institutions and militarists in the general election.

Had the Republican Party nominated an establishment-oriented candidate, Sanders’ supporters might have chosen Hillary, arguing that she is the lesser of two evils. However, the GOP nominated Donald Trump, whose message of economic nationalism, criticism of financial institutions, and oft-mentioned opposition to the invasion of Iraq and the U.S. intervention in Libya made him more palatable to the disaffected voter. Hillary was required to ameliorate the chasm between center-left and liberal Democrats. This was valuable time she could have been using to win over moderates. Consequently, 12 percent of Sanders’ supporters marked ballots for Trump in the general election. Data from Political Wire shows this to be enough to swing the election to Trump.

In addition, some Sanders supporters chose Green Party nominee Jill Stein, Libertarian nominee Gary Johnson, or could just not bring themselves to select Clinton.

Despite Sanders’ request that his supporters vote for Clinton, some saw Trump as more in line with their populist ideologies.

There is a great similitude with the Democratic Party’s predicament in 2016 and 1968. In 1968, U.S. Senator Eugene McCarthy (D-MN), whose flagship issue was ending U.S. involvement in the Vietnam War, lost the Democratic Presidential nomination to Vice President Hubert Humphrey. Humphrey had supported the policies of President Lyndon B. Johnson of continuing the war.

Iowa Governor Harold Hughes and Vermont Governor Philip H. Hoff unsuccessfully beseeched Humphrey to resign as vice president to separate himself from the unpopular administration, but Humphrey instead walked a political tightrope, not wanting to alienate himself from the Democratic establishment, while trying to secure the support of McCarthy supporters.

In part, because of the influence of McCarthy and his vociferous supporters, on Sept. 30, Humphrey announced that as president he would order a unilateral bombing halt in Vietnam “as an acceptable risk for peace.”

Even after that concession, McCarthy did not play the role of a good soldier by publicly supporting Humphrey. Many of McCarthy’s supporters stayed home on election day, unwilling to cast a vote for Humphrey. In fact, McCarthy did not formally endorse Humphrey until a week before the general election. His endorsement finally came as Humphrey, once far behind in the polls, had rallied to being within just two points of Republican nominee Richard M. Nixon.

McCarthy’s endorsement of Humphrey was less than enthusiastic. He proclaimed to his supporters: “I’m voting for Humphrey, and I think you should suffer with me.” McCarthy’s late and tepid endorsement was blamed by some Democrats for Humphrey’s whisker-close loss to Nixon.

Four years later, U.S. Senator George McGovern (D-SD), like Sanders and McCarthy, became a voice for the disaffected Democrats. McGovern overcame 200-1 odds to win the nomination. McGovern staked out territory on the left, supporting “a definite early date for withdrawal of every American soldier from Vietnam,” a $1,000 income supplement for every American, and a major truncation of the U.S. military budget. This message rocket launched him to unexpected frontrunner status. His opponents were forced in the unenviable position of running to his right in the Democratic primary.

Accordingly, Humphrey, running again for the nomination, appeared less progressive, hurting him with liberal voters. After a victory in the hard fought California primary, McGovern secured enough delegates to win the nomination.

In the general election, some moderate and conservative Democrats who supported more establishment candidates in the primary broke ranks and supported Republican Richard M. Nixon in the general election campaign. AFL-CIO President George Meany, who could have been a great help to McGovern, branded him: “an apologist for the Communist world.”

The group known as Democrats for Nixon used Humphrey’s denunciation of McGovern’s primary plan to cut military spending in an advertisement. The narrator states: “Senator Hubert Humphrey had this to say about the McGovern proposal. ‘It isn’t just cutting into fat. It isn’t just cutting into manpower. It’s cutting into the very security of this country.’”

McGovern won only the state of Massachusetts and the District of Columbia. Nixon won 94 percent of Republicans, 66 percent of Independents, and an astounding 42 percent of Democratic voters.

Like 1968 and 1972, the Democratic Party is currently enveloped in a schism between establishment center-left Democrats and liberal insurrectionist progressives. Humphrey in 1968, McGovern in 1972, and Hillary Clinton in 2016 were not able to unify the two bloodlines and lost the general election.

Hillary offers the right diagnosis, that the long primary campaign helped the Republicans in the general election. In addition, the Republicans picked a nominee who was simpatico with Sanders in support of economic nationalism and in excoriating the political establishment. 2016 was a year of political discontent. Both Sanders and Trump were able to capitalize on it. Hillary was seen as a tribune of the establishment and could not convince voters she would be a change agent.