COLUMBIA, SC (CNN) Sen. Bernie Sanders thrashed President Donald Trump, calling him a "racist," and praised Martin Luther King Jr.'s "revolutionary spirit" in a speech here Monday honoring the civil rights leader on the holiday dedicated to his memory.

The Vermont independent's remarks at the King Day at the Dome rally in Columbia, his second visit to the city in three months, come amid intensifying speculation over Sanders' potentially launching a new bid for the Democratic presidential nomination and, if he does, whether he can improve on the dire performances across the South that sunk his 2016 bid.

"Racial equality must be central to combating economic inequality if we are going to create a government that works for all of us and not just the 1%," Sanders said on Monday -- a construction he returned to throughout his address, which contained some of his most pointed remarks on race since he emerged as a national figure three years ago.

Speaking of King, Sanders said, "Yes, he was a revolutionary. And we are going to stand with him by taking on the political and economic establishment and creating a government that works for all of us, not just the few."

Sanders lost badly here in the 2016 presidential primary, and his ability to connect with African-American voters -- to be conversant on racial issues in a way that translates to support at the ballot -- remains a key question as he considers a second run.

"He needs to make sure (his) record is seen in a way that the people here in South Carolina can understand exactly what his commitment is," Rep. Jim Clyburn, a South Carolina Democrat who praised Sanders' work on expanding community health centers, told CNN. "I think he really struggled the last time with that. Hopefully he'll do better this time."

Sanders' allies are hoping for the same.

"The big failure last time is that we failed to plan for our own success. We really didn't think we'd get beyond New Hampshire, certainly not beyond South Carolina," a 2016 staffer who worked for Sanders in multiple states told CNN. "There just wasn't a plan for how to transition staff into those other states. There just became this madhouse dash to help however you could. There wasn't a plan to make it past Super Tuesday. They are trying to do better this time. I know that they're acutely aware of that weakness."

Sanders last appeared in South Carolina weeks before the 2018 midterm elections, when he addressed nearly a thousand supporters at a rally with Our Revolution, the political organization that grew out of his 2016 campaign. Before taking the stage, Sanders met privately with local elected officials and pastors. But his visit was coldly received, or just plain ignored, by state party leaders worried his presence would be used against moderate Democrats ahead of the November elections.

A different set of challenges

Better known now and having picked up some new friends through his post-2016 travels -- perhaps most notably in Florida, where he campaigned for nominee Andrew Gillum before and after the Democratic gubernatorial primary -- Sanders aides are optimistic he will fare better here four years on. After losing every state south of West Virginia and east of Oklahoma in 2016, he could hardly do worse.

in 2016. In his stump speech, and through his policy rollouts, Sanders now regularly and (more) emphatically discusses the economic hardships that disproportionately affect communities of color. An Sanders has made clear efforts to court African-American voters, who broke overwhelmingly for Hillary Clintonin 2016. In his stump speech, and through his policy rollouts, Sanders now regularly and (more) emphatically discusses the economic hardships that disproportionately affect communities of color. An NPR/PBS NewsHour/Marist survey of Democrats and Democratic-leaning independents this month showed the Vermont independent with a 59% approval rating among African-Americans, trailing only former Vice President Joe Biden's 70%. No other potential 2020 contender cracked 50%.

That advantage will likely diminish as voters become better acquainted with the newer names in the field, but Sanders, even in 2016, generally polled well with African-American voters -- especially millennials. The question this time around is whether he can translate those mostly positive feelings into support on primary day.

"He needs to sit down with the leaders across South Carolina who can help him understand the issues that resonate to the primary voter, and I have not heard there is any wide outreach," Amanda Loveday, a former state party executive director and communications director for Clyburn, said last week. "I witnessed Sen. (Cory) Booker and Sen. (Kamala) Harris sit down with legislators and organizers and people who matter when it comes to getting votes in South Carolina. I have not seen him do that."

Sanders followed up his remarks at the state Capitol rally by attending a roundtable with "community leaders and clergy," a gathering organized alongside the state NAACP, at Zion Baptist Church in Columbia. He was scheduled to address a church about an hour away in Florence on Monday evening.

Sanders will continue his South Carolina swing Tuesday by meeting with top state Democratic lawmakers, according to a source with knowledge of his plans. He will join the chairman of the black caucus, state Rep. Jerry Govan, and its members to discuss their priorities before huddling with the state House minority leader, state Rep. Todd Rutherford, and the full Democratic caucus.

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The grassroots work is happening. But the less heady chore of assembling a team on the ground here, and in other early-voting states, has not yet begun. It is a task that will only grow in difficulty as more candidates enter the primary -- Harris announced hours before Sanders' Columbia speech -- and the run on top local operatives begins.

Sanders' prized 2016 Iowa caucus director, Brendan Summers, has already defected to Sen. Elizabeth Warren's camp . A handful of well-regarded operatives who worked for Sanders last time around seem committed to drafting in Beto O'Rourke. Others, like 2016 deputy national press secretary Sarah Ford, are back aboard. Other familiar mid-level operatives are either poised to re-up or being wooed. Stalwart former Iowa campaign coordinator Pete D'Alessandro has said he will sit tight and wait for Sanders to decide. But for an operation that needs to grow, and knows it, the clock is ticking.

If the makeup of a would-be Sanders 2020 presidential campaign remains a mystery, there is certainty in this: Whatever it looks like, the tests ahead will be vastly different from those of its predecessor.

Sanders has already been faced with difficult questions over allegations of sexual harassment among staff on the 2016 campaign, and unlike the last time around, he will face not one but perhaps a dozen formidable opponents. Among them would be at least two or three credible progressive candidates who, though not social democrats in the Sanders mold, share his policy priorities and political style. The 2020 field will also be more racially diverse and, on average, younger. For the women in the contest, Clinton's trailblazing run -- for all its stumbles and ultimate collapse -- went a long way toward destigmatizing and lifting their ambitions.

Those conditions have led some of his own most vocal supporters to suggest that Sanders, and the cause they credit him for elevating, might be best served by his passing up another run.

"The movement needs young blood," Hamilton Nolan wrote on the progressive site Splinter , suggesting that Sanders, 77, should swap the field for the sidelines (though not quite the stands).

New advantages

But among the senator's top aides and his most ardent supporters, there is a differing view of how the coming months and years could play out. It acknowledges the questions -- if not always with concrete answers -- but posits generally that for every new challenge there are fresh advantages.

To start, Sanders now is a known quantity with unrivaled social media and digital operations, which he uses to supplement his traditional media presence, allowing him to reach voters even when Trump is dominating the headlines. His base, though its raw numbers will likely diminish in such a big field, might still be enough to carry him, without any new recruits, through the opening whirl of primary contests. And with most Democrats likely to reject super PAC backing, which can double as life support for flagging campaigns (see: Jeb Bush), this gargantuan Democratic field could shrink sooner rather than later.

Still, his indecision has opened seams for other hopefuls to deliver their messages, without interference, to uncommitted primary voters. Progressive diehards in Iowa and New Hampshire might be undecided between Sanders and Warren, but they have not had to pick which one of them to hear from over the last couple of weeks -- Warren was the only show in town, and she's played in both states to mostly positive reviews.

Some of Sanders' fiercest allies, the progressive or leftist activists and organizers who want him to run, warn that a second bid will have to look much different from its predecessor -- in part because the primary itself will be fought on almost unrecognizable terms.

"Who are you hiring on staff? What types of organizing spaces are they creating early on? Are they, and if they are, how are they listening to the concerns and particular issues that are unique from state to state, demographic to demographic, county to county?" were among the questions posed by Maurice Mitchell, national director of the Working Families Party, which has not endorsed but is typically supportive of Sanders. "It's not any particular speech or buzzword or laundry list of issues, it's an intentionality that's demonstrated in a lot of ways."

The tweaks to the apparatus are beginning to show.

Former campaign manager Jeff Weaver will not return to the job if Sanders runs again, though he remains a trusted senior adviser. The process of picking a replacement is underway, though no choice appears imminent. Nor does an announcement that Sanders plans to run. The uncertain timetable will test the pull of the wider Sanders orbit, including Our Revolution, and other grassroots groups trying to push him in.

Last week, Our Revolution touted the more than 400 house parties organized by People for Bernie and Organizing for Bernie. They spanned all 50 states, Puerto Rico and the Bahamas, and attracted an estimated 3,500 future volunteers. Unlike in 2015, when he was considering a run and progressives were trying to talk Warren into the race, Sanders would enter with more coherent outside support.

"What happened in 2016 is not what will happen in 2020 because there were two separate campaigns -- there was a grassroots campaign that didn't really meet the official campaign until seven months after the official campaign announcement," People for Bernie co-founder Winnie Wong said. "They were playing catch-up with us. That's not the case anymore."

This story has been updated.