The 2020 Iowa caucuses

Some supporters backing non-viable candidates at a Des Moines caucus have decided to band together to support Cory Booker — who dropped out of the race last month.

The move means they declined to support viable candidates like Pete Buttigieg, Elizabeth Warren and Bernie Sanders.

About viability and realignment: At the start of the caucuses, voters split up into groups dedicated to their first presidential candidate of choice. Typically, a candidate needs 15% of the vote to remain viable, as determined by the amount of people participating in the precinct location, but smaller locations may have different viability thresholds.

If a candidate is not viable after that first round, their voters can realign to another viable candidate — or join together to create a group in support of another candidate that meets the threshold.

The Bernie Sanders campaign just opened the door to its watch party as a smattering of people were waiting.

The campaign encouraged supporters not to come to the party until they were done caucusing.

A Democratic state party official tells CNN's David Chalian that they are "doing quality control on results coming in."

The official added that they "should have something near top of the hour."

Joe Biden's campaign has opened the doors at its caucus night party at the Olmstead Center at Drake University.

As the attendees filed in, the campaign turned all of the TVs to CNN, and raised the volume just as Jeff Zeleny reported the former vice president was not viable at his caucus site at the Drake Fieldhouse — on the same campus where Biden’s event is taking place.

There are several dozen attendees on hand at this point.

Facebook on Monday moved to block users from sharing a debunked claim published by Judicial Watch, an activist group that’s supportive of President Donald Trump, about the number of registered Iowa voters. 

The social media platform told CNN it is now appending warning labels to posts that seek to amplify the discredited claims. Users who attempt to share a Facebook post containing the claims will also be interrupted by a notification informing them that the post has false information.

The attempt to limit the claim’s spread follows a fact-check performed by one of Facebook’s third-party partners. When a fact-checking partner flags a piece of content as false, it sends a signal to Facebook, which then automatically acts against the content.

But despite the fact-check, a Facebook advertisement by Judicial Watch that repeated the false claim remained active on the platform until Monday night. According to Facebook’s advertising transparency page, the ad was viewed between 15,000 and 20,000 times nationwide, despite spending less than $100 on the buy.

Asked by CNN Monday night whether the ad would be taken down, Facebook told CNN that “action should be taken shortly.”

Meanwhile, Twitter rejected calls to act against tweets promoting the false claims, saying they did not violate the platform’s policies because the tweets do not "suppress voter turnout or mislead people about when, where, or how to vote.”

 Amy Klobuchar’s campaign manager Justin Buoen tells CNN that their precinct captains say the senator is viable in “a bunch of precincts.”

“Back in the war room, we’ve been talking to precinct captains and they are saying we are viable in a bunch of precincts,” Buoen told CNN.

The realignment phase of caucusing is happening at a caucus site at Grinnell College in Grinnell, Iowa.

Several candidates were not viable, including Joe Biden. Some of his supporters then joined the uncommitted group. The maneuver effectively denies delegates to more progressive, viable candidates, such as Elizabeth Warren and Bernie Sanders.

Pete Buttigieg is also unviable — but many of his supporters remained seated during the realignment. That's when the uncommitted group started chanting "Come on, Pete!"

About viability and realignment: After voters split up into groups dedicated to their first presidential candidate of choice, viability is determined. Typically, a candidate needs 15% of the vote to remain viable, as determined by the amount of people participating in the precinct location, but smaller locations may have different viability thresholds.

If a candidate is not viable, their voters can realign to another viable candidate or join together to create a group in support of another candidate that meets the threshold.

Watch the moment:

Iowa Democratic caucusgoers for whom health care is their top issue in choosing a nominee were split between Bernie Sanders and Pete Buttigieg, with around a quarter supporting each. Fewer than one in five of them were for Joe Biden and Elizabeth Warren, and only one in 10 for Amy Klobuchar.

Two in five say health care was the issue that mattered most in deciding who to support. 

Among caucusgoers who oppose replacing private insurance with a government plan, three in 10 support Biden, and another three in 10 support Buttigieg. Klobuchar’s support is slightly over one in 10 in this group.

Watch more:

Vermont Senator Bernie Sanders came very close to winning the Iowa caucuses in 2016.

Sanders received 49.59% of the vote — a hair away from Hillary Clinton’s winning vote percentage of 49.84%.

Sanders used his Iowa performance to fuel a fundraising boost, raising $3 million from supporters. 

He went on to win the New Hampshire primary by almost 20 points.