Updated at 9:04 a.m. ET
Joe Biden continued his impressive string of primary wins, easily besting Vermont Sen. Bernie Sanders in Michigan, Missouri, Mississippi and Idaho on Tuesday.
With a big delegate lead, he solidified his position as the favorite for his party's nomination to face President Trump in November. Sanders was the projected winner in North Dakota while votes were still being counted in Washington.
"Tonight we are a step closer to restoring decency, dignity and honor to the White House. That's our only goal," Biden said in remarks from Philadelphia.
Pressure on Sanders mounted to reassess how much longer he could wage a campaign after the former vice president racked up more victories by large margins — winning almost every demographic group with the exception of young people.
Sanders returned to his home state Tuesday after canceling an Ohio rally due to coronavirus concerns. He never addressed supporters or the press, and reporters said texts and emails went unanswered.
The biggest blow of the night to Sanders was his crushing defeat in Michigan. Sanders' campaign focused heavily on the state and expectations were high for him to perform better there.
Sanders narrowly won the Michigan primary in 2016, confounding predictions he would lose. That victory served as a huge pivot point for his campaign, which continued its fight against former Secretary of State Hillary Clinton for several more months. Sanders finally endorsed her in July, less than two weeks before the Democratic National Convention.
Democratic turnout in Michigan was dramatically up from four years ago — an estimated half million more voters came to the polls this year.
"A common goal"
Biden focused his comments Tuesday night on a message of "reassuring leadership" as much of the country expresses mounting concern about the Trump administration's handling of the coronavirus contagion. Biden also argued Trump has diminished the nation's standing in the world.
"I believe this nation can overcome four years of Donald Trump, but given eight — four more years can forever and fundamentally change the very character of this nation. We can't let that happen," Biden said.
This week's primary results reinforce the dynamic that fueled Biden's dominating performance on Super Tuesday — Democratic voters rallying behind a nominee they believe can beat Trump this fall.
Exit polls in both Mississippi and Missouri indicated that Democrats voting there viewed the Biden-Sanders race through the lens of a key question: electability.
Sanders' strong ground game, fundraising prowess and dominance among young voters appear to be no match for the widespread perception of Biden as a better match-up against the president.
Biden and his surrogates also argue that he helps candidates in House and Senate races who are worried about the possibility of being on the same ticket as Sanders, a self-described democratic socialist.
Still, Biden made a point to reach out to Sanders and his supporters, saying he needed support from those who backed all of his rivals.
"I want to thank Bernie Sanders and his supporters for their tireless energy and their passion," Biden said, adding, "we share a common goal and together we will defeat Donald Trump."
There were other signs that the race was moving to a new phase.
Guy Cecil, chair of Priorities USA, a Democratic super PAC, had stayed neutral in the race has begun planning for a general election match-up between Biden and Trump.
"What tonight has made clear is that the delegate math is now a straight line to Joe Biden's nomination," Cecil told NPR. "So we're going to do everything we can to help him in the effort looking forward to November."
He said his group was already planning television ads in key states and stressed that all the campaign operations of the various candidates, as well as outside groups, needed to unify and focus in a disciplined way on their key target.
BREAKING: We're all in for @joebiden and for us, the general election starts now. We’re announcing a $2.2 million ad campaign in Pennsylvania featuring Janie, a #Pennsylvania senior who voted for @realDonaldTrump in 2016 but won't be doing so again this November. Why? #healthcare pic.twitter.com/FckHDjwLW2— American Bridge 21st Century (@American_Bridge) March 11, 2020
"We're going to need everybody working together to take on Donald Trump and his conservative allies," Cecil told NPR.
American Bridge, another Democratic outside spending group, announced on Twitter a more than $2 million ad buy in Pennsylvania supporting Biden, a state that Trump won in 2016.
Pressure on Sanders mounts
One of Biden's most prominent surrogates told NPR it was time for the party to shut down the remaining contests and debates.
Rep. James Clyburn (D-S.C.) told NPR Tuesday after Missouri and Mississippi were called for Biden: "I think when the night is over, Joe Biden will be the prohibitive favorite to win the Democratic nomination, and quite frankly, if the night ends the way it has begun, I think it is time for us to shut this primary down, it is time for us to cancel the rest of these debates."
He said without naming Sanders, "You don't do anything but get yourself in trouble if you continue in this contest when it's obvious that the numbers will not shake out for you."
But Rep. Pramila Jayapal (D-Wash.), who has endorsed Sanders, said on NPR that was premature.
"We need to let this play out a little bit," Jayapal insisted. But she conceded late Tuesday that Biden had a good week and "that's going to be a tough thing for Sen. Sanders to confront coming out of tonight."
Sanders' press secretary Briahna Joy Gray tweeted that the move to avoid another debate showed panic in the Biden camp. "America finally gets to see Biden defend his ideas, or lack thereof, on Sunday," when the next Democratic presidential debate is scheduled to take place, in Phoenix.
I, for one, am extremely excited about this debate all the moderates are panicking about.— Briahna Joy Gray (@briebriejoy) March 11, 2020
The delegate count difference is only about 150 points out of 4051 total.
America finally gets to see Biden defend his ideas, or lack there of, on Sunday. #NotMeUs #Bernie2020 https://t.co/g4CYsQIfs6
Even before Biden's latest wins, some of his supporters in Congress worried in interviews with NPR that it would be difficult to bring Sanders' supporters into the tent. Some feared that they could sit on their hands in November or continue public criticism of the former vice president's policy proposals.
Corey Lewandowski, Trump's former campaign manager, predicted on NPR that splits within the Democratic Party would persist, with many Sanders' supporters staying home and assuring the president another victory in the fall.
Sanders has a big platform to make the case for his campaign in this Sunday's debate. While the Democratic National Committee announced there will be no live audience due to coronavirus concerns, it will be the first time he and Biden will be the only two on the debate stage.
Debates have not been Biden's strength in the race for the Democratic presidential nomination. He has been holding shorter campaign events since his dramatic turnaround — a sign that his campaign may be leaving little room for error.
Biden continued to portray himself as the underdog — noting that his campaign was dismissed after poor performance in early states.
"It's more than a comeback," Biden said about his latest wins, "it's a comeback for the soul of the nation."