CHICAGO – It will not be the party convention that President Joe Biden had planned.

A month ago, Biden was on the verge of destroying the Democratic Party. He accepted the nomination with bold claims that he would build on the successes of his first in his second term. Instead, he will open Monday’s convention by arguing that Vice President Kamala Harris is the one who should succeed him.

It is a change of course that Democrats greet with jubilation, melancholy, lingering resentment and, in some cases, outright anger.

Given the complicated dynamics, convention organizers and party leaders had to maneuver carefully: on the one hand, paying respect to the outgoing president, while on the other, building on the party’s renewed enthusiasm for Harris’s rise.

Democrats are expected to honor him in their speeches throughout the week, using what they see as a selfless act as an incentive for the party to rally behind Harris and defeat former President Donald Trump.

Biden is expected to give his speech on Monday and will be the one who can bridge the divide.

It will be “a great opportunity to seize this moment of unity for the party,” said Bill Russo, who worked in Biden’s vice presidential office, on his 2020 campaign and at the State Department. For longtime “Biden people,” a message of unity coming directly from Biden “will help solidify them,” he said. A Monday slot, Russo said, “also gives him a prominent and respected spot that opens the week’s programming.”

The extraordinary personal and political transformation Biden has undergone over the past month is unlike any president in recent history. He has gone from an established party leader to a man who voluntarily relinquished power without being forced to do so by voters or term limits – a rare move in modern politics.

His decision has set the election campaign on a new path. Harris has made strong gains in the polls, attracted 10,000 or more people in the affected states, won hundreds of thousands of new volunteers and caused donations to explode.

But Democrats say the party’s deep gratitude for Biden’s decision is overwhelming, and predict there will be a standing ovation at the United Center when he takes the stage.

“He’s going to have a truly hagiographic farewell convention,” said Wade Randlett, a longtime Democratic fundraiser. “I expect President Biden to be almost deified at the convention, with about 100 speakers lined up saying, ‘Oh my God, Joe Biden is so great.’ And that will increase his overall reputation.”

Senator Mazie Hirono (D-Hawaii) said, “I and others applaud the courage and love of country he has shown in making this very difficult decision.”

A Harris campaign official said: “He won’t be able to speak, there will be so much applause. People in the Democratic Party appreciate him now more than ever.”

Even during Biden’s most difficult term in office, Democrats agreed that he kept his promises. He led the country out of the pandemic and passed a comprehensive infrastructure package. But after a disastrous debate against Trump in late June, doubts grew about Biden’s ability to run a convincing campaign. Within the party, calls for him to drop out of the race grew louder.

In early July, Senator Mark Warner (D-Virginia) reportedly tried to persuade a group of Democrats to call on Biden to withdraw from the race.

“I don’t know anyone who didn’t go into these challenging weeks with the assumption that Joe Biden was a great president and that we owe him a lot,” Warner said.

In gratitude for Biden’s contributions to the party, a number of tributes are planned during the convention, including from Senator Chris Coons (D-Delaware).

Coons said Biden has already initiated plans in recent talks on how he will end his term.

“He’s already looked ahead and talked about what he could accomplish in the last six months of his term and how he could make the biggest impact. He’s asked what I think we should be doing and he’s been positive about Harris’ campaign,” Coons said. “He’s excited about the campaign. I think he’s going to campaign hard in Pennsylvania and elsewhere.”

Chris Korge, national finance chairman of the Harris Victory Fund, said demand for attendance was enormous Monday night as party members wanted to show “their incredible respect for Joe Biden.”

“People are recognizing what Joe Biden has done as president over the last four years, and that is the foundation for why and how Kamala Harris will become the 47th president of the United States,” Korge said. “People are seeing how selfless Joe Biden was. I’ve heard that from so many people who feel like he chose not to run – not because he didn’t think he could win – but because he thought it was the right time for him, and he made the decision to move the next generation forward.”

Some still have strong feelings about the circumstances. One of them is First Lady Jill Biden, who privately expressed dismay at the way some Democrats treated her husband.

“I’ve spoken to 100 Biden supporters, from representatives to senators to members of the National Finance Committee, who believe he was completely screwed,” said a source familiar with the internal discussions, who asked to remain anonymous to reveal private conversations. “It was unfair, it was unwise, it was unjust. The people who did it will not look back well on this historic moment because of their own behavior. … I have a lot of resentment toward the people who pushed Joe out, but Kamala Harris is not one of them. She was not a Judas at all.”

Chris Dodd, a former senator from Connecticut and close friend of Biden’s who had just spoken to him on the phone, said Biden is looking forward and not focused on expressing his displeasure.

“I would be shocked to hear that Joe Biden, the person I know, walks around with a grudge against people,” said Dodd, who has been friends with the president for 50 years. Dodd said he hopes the tributes arriving Monday will touch Biden both as a person and commemorate his time in office. “In 50 years in public life, I can honestly say that I don’t know if I’ve ever met anyone in public life who was as decent, as kind, as considerate as President Joe Biden.”

This article was originally published on NBCNews.com.