Bernie Sanders endorsed Hillary Clinton on 12 July 2016, but did not suspend his campaign.
FDR had a majority of delegates heading into the 1932 convention, just not enough to secure the nomination without a fight. Roosevelt's endorsement of a rival candidate is undocumented.
On 12 July 2016, Democratic presidential candidate Bernie Sanders formally endorsed rival Hillary Clinton at a New Hampshire event, causing consternation among supporters who were confident he still planned to take his candidacy for the nomination to the convention in Philadelphia later that month.
A number of interlinked rumors appeared on social media following the Clinton/Sanders event, roughly outlining a larger general claim. According to many social media users, Sanders' pre-convention endorsement was a requirement under Democratic National Committee (DNC) rules as a condition of bringing his delegates to the convention, just as Franklin Delano Roosevelt had similarly been forced to endorse an opponent before going on to win at a contested convention:
I have contacts within both campaigns. Here’s what I was told yesterday and today. Clinton’s campaign “threatened” to vote down every concession made to Bernie on the platform if he did not endorse her prior to the convention. Knowing that Superdelegates were not going to switch to his side without something major happening, the best he could do was hold on to the progressive concessions he won for US on the platform. He could not, in good consciousness let the GOP and Trump win, especially when we have a potential half of the Supreme Court Justices that will be replaced within the next 4-8 years. He was looking out for the future of our movement and our nation in this very hard decision he made. This post is not to tell you to vote for Hillary, or to not leave the Democratic Party, etc. this was just to throw a little light on why Bernie did what he felt he HAD to do, rather than what he wanted to do. A sign of a great leader is someone who makes the hard decision to sacrifice themselves for the people and movement behind him. He is counting on us to continue the fight.
Contacted later in the day by phone, Wolthuis clarified her comments about the use of force and Sanders' endorsement of Clinton:
[A]fter reaching out to many of the people who had either posted or tweeted this statement, I tracked down the original source, Ashley Wolthuis, a Sanders delegate from Utah, who was kind enough to return my "cold call" to her cell phone. Here is what she told me.
The basic thrust of the post shown above is accurate, she said, but the use of the term that Bernie was "threatened" she explained was overblown. She did indeed have conversations with various delegates associated with both campaigns, and she said it was "common knowledge" among most delegates that the Clinton campaign was insisting on Bernie making an endorsement prior to the convention if the more progressive parts of the platform would be retained. The talk among her the those with whom she associated, both Clinton and Sanders supporters, was that Bernie understood Hillary needed Sanders' supporters and that was the only reason she made any concessions at all regarding the positions on the DNC platform for which the Sanders campaign fought.
Wolthuis also referenced a Washington Post article published after Sanders' 12 July 2016 comments, surmising that Sanders in part intended to tack Clinton to promises of a progressive platform:
The speech today was, ostensibly, an endorsement of Clinton's presidential campaign ... But, really, it wasn't. Yes, I know that's how it was billed by the Clinton and Sanders camps. And, yes, he did say this: "I have come here to make it as clear as possible as to why I am endorsing Hillary Clinton and why she must become our next president." (It was the only time that Sanders used the words "endorse" or "endorsing" in a speech that ran 2,161 words. You can read the whole thing here.)
But, surely, Sanders was simply touting his successes as a way of winding up to the big moment when he acknowledged — even subtly — that Clinton's more moderate, cautious and pragmatic definition of "Democrat" had trumped (ahem) his more liberal, populist one? ... Nope! Not really. What followed in the speech was a laundry list of Sanders's talking points and policies supplemented with the phrases "Hillary believes" or "Hillary understands" or "Hillary knows" stuck in front of them ... On and on it went, Sanders touting a much-beloved policy of his and then noting that Clinton agreed with it.
We reviewed the oft-cited DNC 2016 rules [PDF] but were unable to locate any specific verbiage mandating that any candidate endorse any other candidate in order to fully participate in the convention. It is possible (but not necessarily likely) that the endorsement was an agreed upon concession made outside formal rules or quietly between the campaigns. Confusion over the meaning of Sanders' endorsement was exacerbated following the release of the contents of a conference call he held with his nearly 1,900 pledged delegates hours after his public appearance alongside Clinton:
During the 38-minute long call, Sanders maintained the campaign won 22 states and lost several more "by a hair," stating that a majority of voters under 45 from all demographics overwhelmingly voted for him in primaries and caucuses. Sanders held that the "superdelegate issue" impeded his campaign, noting that Clinton earned 2,205 pledged delegates to his 1,845 and that she received "a hell of a lot" more superdelegate support:
In a portion of the call regarding his endorsement of Clinton, Sanders did not say that doing so was a condition of bringing his delegates to the convention. He did, however, discuss ongoing negotiations between the campaigns to ensure that planks of Sanders' campaign were adopted and Clinton was "on record" making such agreements. Compromises cited by Sanders included the candidates' differing plans on college tuition and single payer healthcare (including dental and mental health coverage) expansions for millions of Americans. In a significant portion of the call Sanders addressed questions about delegates' traveling to Philadelphia for the convention, asserting the campaign "[needs its delegates] to vote for Bernie Sanders for President, and [his] hope is we can get 1,900 votes on the first ballot."
Sanders addressed rumors of challenges to credentials without further detail, presumably referencing concerns that Sanders delegates would face opposition at the convention. The senator stated he didn't believe the rumors had merit, adding that the campaign would arrive with "a bunch of lawyers" in Philadelphia and "make sure every [delegate takes their] seat." Sanders also addressed questions about whether he had been offered a "significant role" in a potential Clinton administration, to which he said "no." Towards the end of the call, Sanders stated that his campaign was not suspended, but that he expected Clinton to emerge as the nominee following the convention.
Overall, the conference call represented the most in-depth look regarding Sanders' motivation in endorsing Clinton prior to the convention. No portion of the call hinted or suggested that his endorsement was due to tacit threats or coercion with respect to negotiated agreements between the campaigns.
A second portion of the rumor held that Sanders was heading into a contested convention having endorsed his rival, just like FDR before him. Rumors to that effect didn't specify when or under which circumstances Roosevelt made such an endorsement before going on to win the nomination (if a year was cited for this occurrence, it was typically 1932). A 2007 New York Times article about FDR's 1932 convention win did demonstrate many parallels to the contest between Clinton and Sanders:
In 1932, the leadership of the Democratic National Committee was firmly in the hands of Al Smith loyalists. Convention rules required a two-thirds majority for nomination, and the party’s last three presidential candidates — James Cox of Ohio, the Wall Street lawyer John W. Davis and Al Smith — in addition to House Speaker John Garner and Senate minority leader Joe Robinson, were on record supporting the stand-aside economic policies of the Hoover administration and the ill-conceived and exorbitant Smoot-Hawley tariffs on imported goods.
Roosevelt was an outsider. Serving his second term as governor of New York, he could not even count on the solid support of the Empire State’s delegation at the convention ... all of F.D.R.’s rivals were from the pro-business, hard-money, establishment wing of the Democratic Party and decried the possibility of government intervention to revive the economy. “Let natural forces take their course, as free and untrammeled as possible,” said Governor Ritchie.
“Modern society, acting through its government,” said F.D.R., “owes the definite obligation to prevent the starvation or dire want of any of its fellow men and women who try to maintain themselves but cannot.”
The conservative wing of the Democratic party was aghast. “I will take off my coat and fight to the end against any candidate who persists in any demagogic appeal ... setting class against class and rich against poor,” rasped Al Smith.
However, a substantial difference existed between Roosevelt in 1932 and Sanders in 2016. In addition to facing a three-way runoff requiring a two-thirds majority, Roosevelt (unlike Sanders) went into the convention with a majority of delegates (but no superdelegates, as that concept was not introduced until 1984):
When the convention opened on June 27, Roosevelt held a clear majority of delegates but was still 100 votes shy of the two-thirds required for nomination. If the establishment forces could deny F.D.R. a first-ballot victory, they might deadlock the convention and force a compromise choice. The Democratic party’s two-thirds rule was the nemesis of presidential front-runners, and in the eyes of the party’s old guard, Roosevelt was ripe for a fall.
Nevertheless, F.D.R.’s majority gave him control of the convention. His candidate for presiding officer, Sen. Thomas Walsh of Montana, was elected, and the credentials of three pro-Roosevelt delegations (Louisiana, Minnesota and the Virgin Islands) were accepted.
No portion of that article mentioned Roosevelt "endorsing" his rival, merely tensions between "establishment" Democrats and an "outsider" candidate. Another article described aspects of the nominating process with which Clinton had more in common with Roosevelt than Sanders did:
The vote was split enough to guarantee a brokered convention; FDR’s camp arrived in Chicago with a majority of delegates but not enough to guarantee him the nomination.
Given FDR's majority of delegates and votes, it was exceedingly unlikely he at any point endorsed either of his rival candidates (of whom there were two). Moreover, journalism and political news operated far differently in 1932 than 2016, making an "endorsement" tendered by FDR for a rival far less relevant than in the era of social media. It was true Sanders in some respects evoked Roosevelt's position at the contested convention of 1932, but the material difference between Sanders in 2016 and FDR in 1932 boiled down to a majority of delegates. (We contacted archivists at the FDR Presidential Library & Museum for confirmation that Roosevelt did or did not endorse a candidate in 1932 prior to winning what was a hotly contested convention. An individual with whom we spoke indicated that detailed information was not to hand, adding that an archivist would look into the claim and respond to our query.)
In short, it isn't precisely clear why Sanders opted to endorse Clinton weeks before the convention without suspending his campaign. Many Sanders supporters maintained that the DNC or Clinton campaign threatened to rescind platform promises had Sanders not endorsed, but the senator made no such claim himself in a 12 July 2016 delegate conference call. During that call, Sanders did urge all delegates to appear in Philadelphia and vote for him on the first ballot.
As for claims that Sanders (like FDR before him) was heading into a contested convention after endorsing a rival, there was scant truth to that claim. FDR headed into the convention with a majority of pledged delegates, prior to the advent of superdelegates. While FDR needed a hard-won two-thirds majority to seize his nomination, he also started with more delegates than his competitors. And the process of formally endorsing a rival didn't appear to be exceptionally relevant (if at all common) in the 1932 presidential nominating process.