After adding in the remaining sixteen contests, FiveThirtyEight estimates total Democratic primary and caucus turnout for 2016 will hover somewhere around 28.7 million total votes. According to current projections, Sanders will end up with anywhere from 12-14 million of those total votes. Assuming a consistent 30 percent of Sanders supporters are #BernieorBust, around 4 million Sanders voters would refuse to support Hillary Clinton in November.

While 4 million votes may not sound like a lot for a country with over 300 million people, it’s enough to swing a close election. And even if the 4 million figure seems inflated by optimistic projections, John Kerry lost to George W. Bush by just 3 million votes in 2004, which even by a conservative estimate (25% of 12 million) fits the current size of the national #BernieOrBust movement. And of course, Al Gore actually won the popular vote by just over half a million votes in 2000, but lost the electoral vote due to the close margins.

And while the 2008 and 2012 elections were landslide victories for Barack Obama, he had the support of almost all black voters and nearly half of white voters, young and old voters, men and women, and most independents, Southerners, Westerners, and Northeasterners. It’s important to note that in 2016, the demographics Obama won in both elections are now split into coalitions evenly divided between Hillary Clinton and Bernie Sanders. Clinton will need as many Sanders supporters as possible to defeat the eventual Republican nominee.

Furthermore, the Democrats were galvanized immediately following the disastrous Bush presidency in 2008, and Obama was running as an incumbent in 2012. Neither of those factors are at play in the current race.
Like it or not, Clinton won’t be able to defeat a Republican without the 4 million #BernieorBust voters. So yes, the #BernieorBust movement will likely prevent a Clinton victory, ushering in at least four years of a Republican presidency and a Republican supermajority in Congress.