Ahead of a roll call vote on Tuesday night, Bernie Sanders spent the morning lobbying his delegates, calling for unity and urging them to join him in backing Hillary Clinton as a bulwark against the prospect of President Donald Trump.

Sanders delegates—many of whom could be seen weeping as their candidate addressed the Democratic National Convention (DNC) on Monday night—will have one last chance to register their support for the Vermont senator's presidential campaign during a roll call vote on Tuesday evening, when Clinton is expected to formally secure the Democratic nomination.

During his speech Monday night, Sanders told his grassroots army that he welcomed those roll call votes, and both Sanders and Clinton campaign officials have confirmed as of Tuesday morning that all 57 states and territories will have their voices heard.

ABC News explains how the process works:

Both Clinton's and Sanders' names were placed into nomination for president at the DNC, largely a symbolic gesture for Sanders supporters. They will have 20 minutes of floor time to make speeches about the Vermont senator and Clinton.

In order to be technically placed for nomination, a candidate had to personally give his or her written approval to the convention secretary along with 300 signatures by 6pm Monday. Both Sanders and Clinton did that.

[...] Every state is called upon alphabetically and a selected delegate or official from each state will speak before announcing how the state’s delegate vote should be allocated.

According to MSNBC producer Kyle Griffin on Twitter, "negotiations are underway to have Bernie Sanders officially nominate Hillary Clinton at the end of tonight's roll call."

Meanwhile, Sanders made surprise appearances at several state delegation gatherings on Tuesday morning, echoing his message that Donald Trump "is a disaster." 

To Florida delegates, Sanders said of Trump, "This man has a unique feature that not all Republicans share by any means: He is a demagogue, a bully, and somebody that does not believe in the Constitution."

Addressing the New York delegation, Sanders added: "Our first task in the next few months and I know we'll all work on, is to see that Secretary Clinton gets elected, but our second task is never to lose focus on the most important issues facing the working families of this country. And our third issue is to make sure this country does not move toward a political oligarchy where a handful of billionaires spend hundreds of millions of dollars electing candidates to represent the rich and powerful. Together we will overturn Citizens United."

.@BernieSanders at New York delegation breakfast: The Democratic Party "needs to open its doors" #DemsinPhilly https://t.co/clR5O1uV9s

— ABC News Politics (@ABCPolitics) July 26, 2016

"Elections come and go. What we must do, or forever look back in regret, is defeat Donald Trump and elect Hillary Clinton," he told California delegates. "It is easy to boo, but it's harder to look your kids in the face who would be living under Donald Trump."

Still, some Sanders delegates weren't convinced by their candidate's speech in which he said he was "proud to stand with her."

"I respect the decision to endorse Hillary Clinton, but I am definitely not any more for Hillary than I was before his speech," 22-year-old Sarah Hernandez told the Guardian on Monday night.

But Sanders' message seems to have landed for some.

"There is nothing radical about failing to take a stand on a far-right racist demagogue sweeping to power in what remains the world's most powerful nation," Guardian columnist Owen Jones wrote on Tuesday. "The election of Trump would represent one of the greatest calamities to befall the west since the end of the second world war. The task ahead is to ensure Trump's defeat—as decisively as possible—and Democratic control of both Houses of Congress, and then to build pressure from below to enact progressive legislation."