WASHINGTON — A day after Hillary Clinton made history by claiming the Democratic presidential nomination in front of a throng of boisterous, flag-waving supporters, the work of unifying her party got underway in a windowless hotel conference room where signs and outbursts were strictly prohibited.
As Bernie Sanders faced mounting pressure to abandon his campaign after losing primaries in California, New Jersey and two other states Tuesday, a group of 15 Democrats opened a lengthy discussion about whether and how the Vermont senator's candidacy would change the party's platform ahead of the general election in November.
Clinton and party leaders want to join together quickly and focus their energy on presumptive Republican nominee Donald Trump, but they must also find a way to harness the passion and devotion inspired by Sanders' insurgent campaign.
Drafting a more progressive party platform than the one adopted in 2012, when President Barack Obama won his second term, will be part of that effort.
"We've got to get to a place where we have a platform that we can all believe in, a set of issues we can all get behind," said Ben Jealous, a Baltimore businessman and former NAACP leader who became a top surrogate for the Sanders campaign. "It'd be very hard for us to win if we can't motivate our entire base."
Some Democrats on Capitol Hill were increasingly outspoken Wednesday in nudging Sanders to wind down his campaign and throw his support behind Clinton.
Sanders, who won primaries in North Dakota and Montana on Tuesday, is set to meet with Obama on Thursday. The president is expected to endorse Clinton soon after.
Democratic Sen. Bob Casey of Pennsylvania said it is time for the party to unite, and Sen. Bill Nelson of Florida said Sanders should "stand down."
Uniting is proving no easier for Republicans, who have been swept up in the controversy around Trump's repeated assertion that a federal judge's Mexican heritage made him incapable of impartiality in the Trump University cases. Some GOP leaders, including House Speaker Paul Ryan, have described the comments as racist.
But the avalanche of Republicans abandoning Trump that Democrats have pined for has not materialized.
The New York businessman delivered a focused, scripted speech after his victories on Tuesday that seemed aimed at reassuring GOP leaders. Despite Ryan's earlier concerns, the speaker reaffirmed his support for Trump in a closed-door meeting Wednesday.
The GOP will also draft a platform, but the party has not yet held public hearings.
Democrats heard from nearly two dozen speakers Wednesday at a Washington hotel in the first of several such meetings to develop the platform. Those offering testimony included James Obergefell, the plaintiff in the landmark Supreme Court case last year that legalized same-sex marriage, former Attorney General Eric H. Holder and Lucia K. McBath, mother of a 17-year-old high school student from Florida who was shot to death in 2012 over the volume of his music.
Despite the energy of the primary, and the contempt Sanders and Clinton supporters have sometimes displayed for one another, the meeting Wednesday was subdued. The several hundred attendees were warned against large signs and noisemakers, and those who spoke were asked to refrain from overtly political statements.
As the meeting entered its third hour, only a few dozen people remained.
A party's platform — a lengthy document that outlines positions on a wide range of policies — is not binding on its nominee. But it helps define the party's vision for its members and the wider voting public, and can have an impact on the debate in down-ballot races across the country.
"It establishes clear water between the Democrats as a group and the Republicans as a group," said David Coates, a political scientist at Wake Forest University.
Sanders has already pushed Clinton to the left on some issues, including increasing the federal minimum wage.
But Sanders supporters will likely want the platform to call specifically for a $15-an-hour federal minimum wage — higher than Clinton has supported. They might also seek stiffer Wall Street regulations and stronger opposition to free-trade agreements.
Those who offered testimony made many other requests. Washington Mayor Muriel Bowser said Democrats should embrace a plank calling for statehood for the District of Columbia. Jealous said the party should support an end to the death penalty (the 2012 platform said the death penalty "must not be arbitrary").
Campaigns generally negotiate the contours of a platform behind the scenes before the nominating conventions, but observers say the committees involved also have influence.
For now, the greatest challenge for Rep. Elijah E. Cummings, the Baltimore Democrat who chairs the drafting committee, is to ensure that both Sanders and Clinton supporters view the process as fair.
Sanders has often complained that party officials have been quietly pulling for Clinton all along. If his voters get the sense that the system is rigged, they might stay home in November.
Cummings has endorsed Clinton but has a long relationship with Sanders.
"We want to make it clear to every American, your voices will be heard," he said.
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The process, Cummings said, will be "inclusive, fair, transparent and reflective of our entire — entire — party."
But Stan Merriman, a party volunteer from Delaware, said he was disappointed that only a few people were allowed to testify on Wednesday. First in line to enter, the 79-year-old Clinton supporter was stopped by security as he attempted to distribute his testimony to a group of reporters.
Handouts, Merriman was told, were not allowed. He was encouraged to submit his thoughts via a website instead.
"This was kind of contrived and slapped together," Merriman said, "but I'm glad it's being done."
The Associated Press contributed to this article.