After a Southern California union threatened to protest next week's Democratic presidential debate, all seven of the White House hopefuls who qualified for the stage have since vowed not to cross the labor group's picket line, "even if it means missing the debate," reports CBS News campaign reporter Alexander Tin.

"While we remain hopeful that the labor dispute can be resolved before next Thursday, we want to be clear that if the situation remains unresolved there could be picketing on the evening of the debate," the leadership of UNITE HERE Local 11 wrote in a letter to candidates Friday, citing a breakdown in talks with Sodexo, the food service provider at debate host Loyola Marymount University.

The potential boycott presents a quandary for the Democratic National Committee, which had already moved the event once before in November over another California union's concerns. With less than a week until the race's sixth debate, a second location change could pose a massive logistical hurdle for the party.

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In a statement, debate host Loyola Marymount University says they are not "party to the negotiations" and have asked the company to meet with the union next week in hopes of a solution. In their statement, Sodexo insists that they are "100% committed to reaching an agreement" with the union.

REACTIONS TO BORIS

President Trump characterized the British Prime Minister Boris Johnson's win in Thursday's elections as a "harbinger of what's to come" for 2020, reports CBS News broadcast associate Aaron Navarro. Some of his more moderate Democratic challengers agreed, and said the success of the conservative party in the United Kingdom should worry some of their more left-wing rivals. New York City mayor Michael Bloomberg called it "a sort of catastrophic warning to the Democratic party."

"You're just going to have to have somebody that can beat Donald Trump and that is not going to be easy. Americans want change, but I think they don't want revolutionary change, they want evolutionary change. They want change that includes everyone. They want change that they can understand and that's exactly the kind of campaign that I would run," he said in Alexandria, VA during an unveiling of his clean power plan, reports CBS News campaign reporter Tim Perry.

In a live interview with the Washington Post, South Bend Mayor Pete Buttigieg, considered one of the more moderate Democratic candidates, said it's a bit tougher to draw comparisons between the two countries due to Brexit, which he said is "just different than anything going on in the United States." He also said the political spectrum is a bit hard to compare as well, and that a "conservative in a place like the U.K. would probably be considered a center-left Democrat in a place like the U.S. The climate policies, even a lot of the health and social policies that are considered more right or center-right over there are not at all welcome in today's American Republican Party."

At a California fundraiser on Thursday, Vice President Joe Biden predicted a Johnson win, according to the press pool report, and that the headlines would read, "Look what happens when the Labour Party moves so, so far to the left. It comes up with ideas that are not able to be contained within a rational basis quickly."

FROM THE CANDIDATES

MICHAEL BLOOMBERG

Former New York Mayor Michael Bloomberg traveled to Alexandria, VA on Friday to unveil his first of several upcoming plans to "propel the country towards a 100% clean-energy future as soon as humanly possible, and before 2050." His new plan outlines steps toward cutting emissions by 50% and a vow as president to "immediately stop new construction of gas plants and retire all U.S. coal plants in the next decade."

Originally scheduled to hold an event with local climate activists and volunteers at the decommissioned Potomac Generation Station, formerly known as the GenOn plant, the event was moved indoors due to rain. The power plan was once brought to national attention when Bloomberg donated $50 million from his charitable foundation to support efforts of closing down the country's coal-fired plants.

Perry attended Bloomberg's event, where he continued to strike a tone of moderate change instead of some of the drastic changes that are being brought forward by some of the more progressive candidates seeking the Democratic nomination.

"My experience in business and 12 years in City Hall running the most progressive city in the country was: if you set big long term goals, nothing ever happens. If you set small achievable goals, you can do 'em one after another," Bloomberg said, making a slight jab at some of the more ambitious goals like the Green New Deal that garner some support among progressives within the Democratic Party.

"It's just amazing when you stop down the road and look back and see the compounding effect of doing lots of small things. It's really quite amazing. You get where you want to go with a lot more assurance and a lot quicker."

Other details of the plan include a goal to make 80% of electricity-generation in the U.S. to come from clean sources by 2028, replacing all coal plants with clean energy by 2030, create "millions of jobs," out of a new clean energy economy and an investment in communities that have suffered the most from coal pollution. Though the plan does not list a price tag, Bloomberg said much of what he's proposing has already been done and they tend to be, "not all that expensive."

"We've already closed 299 out of 530 coal fired power plants in America. I think the number's about 70 coal fired power plants in Europe out of 320 and we just started working there," he said. They added, "And my foundation basically funded it all. So it wasn't that much money."

CORY BOOKER

New Jersey Senator Cory Booker released his education plan Friday morning. The plan includes a $200 billion investment to improve school infrastructure. A Booker administration would also triple funding for Title I schools, reports CBS News campaign reporter Jack Turman. Booker also plans to raise teacher pay up to $15,000 for teachers serving in high-poverty districts. A Booker administration plans to achieve this goal by passing Booker's RAISE Act. The plan also indicated Booker's support for quality public charter schools.

"Every parent in America hopes that their child will have the opportunities that come from a great public education. The education I received as a child transformed the trajectory of my life," Booker said in a statement.

"But to get it, my parents had to fight to move my family into a neighborhood with good public schools. 50 years later, the reality is that access to a high-quality public education still too often depends on the zip code a child lives in and the size of their family's bank account."

STATE-BY-STATE

IOWA

Senator Amy Klobuchar announced two more endorsements in Iowa from State senator Kevin Kinney and State representative Sharon Steckman, report CBS News campaign reporters Musadiq Bidar and Adam Brewster. Kinney said Klobuchar's "track record of working across the aisle and prioritizing rural communities is second to none." He added that Klobuchar is "uniquely" able to connect with Iowans and voters in the Midwest who have "felt overlooked in recent years."

Kinney currently serves as the ranking Democrat on the State Senate's Agriculture Committee. Steckman represents parts of Northern Iowa and was elected as Assistant Minority leader in 2018. She said she's campaigned alongside a number of candidates in recent months but believes that Klobuchar "has the agenda, vision and determination to make a difference for rural communities."

The former President of the Iowa State Education Association, Dr. Tammy Wawro, announced she is endorsing Vice President Joe Biden. "It is critical to have a president our children can look up to again and that is Joe Biden," Wawro, a current teacher in Cedar Rapids, said. Wawro said there's no candidate in that race who will be a better champion for teachers and students than Biden. "As the spouse of an educator, Joe will treat teachers with the dignity they deserve and he'll nominate a Secretary of Education who has experience in the classroom."

SOUTH CAROLINA

While CBS News has continued to report on former Vice President Joe Biden's steady lead in South Carolina, a Post & Courier/Change Research poll shows Biden ahead of the Democratic field by only 7%. In a survey with 392 likely Democratic primary voters in the state, Vermont Senator Bernie Sanders came in second and was ahead of Massachusetts lawmaker Elizabeth Warren by 1 percentage point.

According to the Post and Courier, Sanders gained the most support—with 7%--of any candidate since their last poll in October. CBS News campaign reporter LaCrai Mitchell reports that Sanders' South Carolina team credits in part, their outreach to over 800,000 individual voters in the state.

"The Senator has raised the most money in South Carolina, we have the most individual donations in South Carolina of any candidate, in Q3 we saw those numbers triple from Q2," said Sanders South Carolina Communications Director Michael Wukela. "We have the largest staff in South Carolina of any candidate, we have new Latino endorsements—take that altogether and there's no denying that Sen. Sanders is surging and we have the momentum."

NEVADA

The Culinary Union is denying allegations made by one of its shop stewards that a paid organizer rallied hecklers, at an event with Bernie Sanders on Tuesday in Las Vegas, with chants of "union healthcare" during the Vermont senator's explanation of his Medicare for All platform, reports Tin. The labor group's leadership has long voiced skepticism over the single-payer proposal, saying that its membership opposed the plan.

"Workers chanted affirmatively for candidate's positions at times, verbalized their opinions on issues, and voiced support for their union healthcare, all of which is to be expected in a town hall format," a Bethany Khan, a spokesperson for the union, tells CBS News in a statement. "We encouraged town hall attendees to listen to all the candidates and be respectful."

FOR FUN

While the House of Representatives is set to vote on articles of impeachment against President Trump in the coming days, CBS News' campaign reporters deployed in Iowa, New Hampshire and South Carolina say they aren't seeing impeachment come up as a main topic of interest for Democratic voters in early-voting states.

"I've heard a grand total of two questions [about impeachment], and I've probably heard hundreds upon hundreds of questions from voters," CBS News campaign reporter Nicole Sganga said on "The Takeout" this week of her coverage in New Hampshire.

Bidar and Mitchell, who have spent months covering the 2020 Democratic candidates for CBS News in Iowa and South Carolina, respectively, agreed.

"In the past three months, I can think of one town hall where impeachment has come up," Mitchell said. The reporters said that based on their conversations with voters across the three states, the biggest issues for voters in the early-voting states are access to healthcare, immigration and criminal justice reform, as well as the opioid epidemic.

Mitchell, Sganga, and Bidar joined CBS News chief Washington correspondent Major Garrett on this week's episode of "The Takeout" to discuss what they have heard from voters thus far in the Democratic primary process.

For more of Major's conversation with Sganga, Mitchell and Bidar, download "The Takeout" podcast on iTunes, GooglePlay, Spotify and Stitcher. New episodes are available every Friday morning. Also, you can watch "The Takeout" on CBSN Friday at 5pm, 9pm, and 12am ET and Saturday at 1pm, 9pm, and 12am ET. For a full archive of "The Takeout" episodes, visit www.takeoutpodcast.com. And you can listen to "The Takeout" on select CBS News Radio affiliates (check your local listings).

IN THE HOUSE

A Bernie Sanders endorsement for "Young Turks" creator Cenk Uygur in California's 25th district special election was quickly rescinded after backlash, stemming from Uygur's history of what critics called offensive and sexist comments, reports Navarro. Sanders endorsed the candidate on Thursday but walked it back on Friday.

"As I said yesterday, Cenk has been a longtime fighter against the corrupt forces in our politics and he's inspired people all across the country. However, our movement is bigger than any one person. I hear my grassroots supporters who were frustrated and understand their concerns. Cenk today said he is rejecting all endorsements for his campaign, and I retract my endorsement," he said in a statement.

In a series of Tweets, Uygur criticized "corporations, lobbyists, and special interest groups" for the backlash against Sanders and said "That's why I have decided that I will not be accepting any endorsements…The only endorsements I'll be accepting going forward is that of the voters."

Uygur's Democratic opponent, Christy Smith, has also been collecting endorsements ahead of March 2020's primary. House Speaker Nancy Pelosi was one of the latest big names to do so, and Smith already had backings from Representative Adam Schiff and Senator Kamala Harris, as well as California Governor Gavin Newsom. The state's Democratic party will vote to back a candidate on Saturday.

IN CASE YOU MISSED IT…

Here is a roundup of the Political Unit's reporting for CBSN and CBSNews.com this week:

CBSN

· Booker receives over $1M in campaign donations // By Adam Brewster

· 2020 candidates weigh in on impeachment // By Sarah Ewall-Wice

CBSNews.com

· "Solidarity": 2020 candidates vow to boycott December debate to support union protesters // By Alexander Tin

· Joe Biden gets major South Carolina endorsement from former Harris backers // by LaCrai Mitchell and Caitlin Huey-Burns

· Trump fires back at Democrats over articles of impeachment: "This is impeachment light" // By Eleanor Watson and Victoria Albert

· McKinsey to allow Buttigieg to disclose identity of his consulting clients // By Jack Turman

· Pete Buttigieg to allow access to closed-door fundraisers // By Jack Turman

· Pete Buttigieg releases list of McKinsey clients // By Jack Turman

· House Democratic campaign arm launches digital battleground ads to protect vulnerable incumbents // by Aaron Navarro

· Bush grandson runs for Congress in Texas // by Aaron Navarro

· What Democratic primary voters are talking about in early-voting states // by Jake Rosen feat. Nicole Sganga, Musadiq Bidar & LaCrai Mitchell