The event scheduled for this Saturday has now been moved to a room at the Phoenix Convention Center, which spans a massive 123,500 square feet.
It is currently unclear how many have RSVPed or plan to attend via his website, but judging by the upgrade it is safe to assume they have had a large response. The Facebook event page currently indicates 3.4K plan to attend, and posts to the page suggest that over 9,000 have RSVPed through the form on the website.
According to the RSVP page for the event on the candidate's official website, Sanders plans to speak on getting big money out of politics, dealing with obscene wealth and income inequality in the US, combatting climate change, and making college education affordable for all.
Last weekend in Phoenix, GOP candidate Donald Trump also had to rebook his rally to accommodate rising demand to attend. His campaign stop was originally slated for the luxurious Arizona Biltmore Resort and Spa, but was also moved to a room at the Phoenix Convention Center.
Trump’s event took place inside the North Building Ballroom, which holds a maximum of 4,200 people and spans 45,600 feet — tiny compared to the room in which Sanders is now scheduled to speak.
The Washington Post estimated turnout for Trump’s event around 4,200; CNN was more generous estimating 5,000. Trump himself has multiplied that, though, with claims ranging from 10,000 to 20,000.
After being called out by many news outlets for exaggerating, Trump tweeted: "Convention Center officials in Phoenix don't want to admit that they broke the fire code by allowing 12-15,000 people in 4,000 code room."
Despite Trump’s claims, it appears that Sanders still holds the record for the largest turnout of any presidential candidate so far, with his massive rally in Madison, Wisconsin, which saw 10,000 attendees.
Sanders, once thought a long-shot candidate for the Democratic presidential nomination, has seen a ten-point gain in polls, while frontrunner Clinton has dropped nine points since April.