Columbia, South Carolina (CNN) In his first visit to South Carolina as a 2020 candidate, Joe Biden bragged about "my buddy Barack." He warned of "Jim Crow sneaking back in." And he mocked President Donald Trump, calling him a "clown."

The former vice president this weekend made his opening trip through what might be the most important state in his path to the Democratic nomination. It's where he'll attempt to leverage two advantages he has over the rest of the primary field: Decades-long relationships with party leaders and his early strength with black voters -- who are likely to prove decisive here and in other southern-state contests.

Black voters made up 61% of the Democratic primary electorate in South Carolina in 2016. And Hillary Clinton's strength with those voters -- she captured 86% of their support to Vermont Sen. Bernie Sanders' 14% -- was a preview of how Clinton would ultimately win the party's nomination.

This time, Biden begins as the front-runner with non-white voters -- with 50% support among the group in a CNN poll released last week , compared to his 39% support overall. But he faces a deeper and more diverse field of lesser-known contenders, including two black candidates in California Sen. Kamala Harris and New Jersey Sen. Cory Booker.

In an interview with The Post and Courier , Biden said the state is crucial to his chances of winning the Democratic nomination -- and emphasized being the vice president to the nation's first black president, Barack Obama.

"When Barack and I worked together, we spent a lot of time trying to figure out how to change the systemic racism that exists and continue to work on that," Biden said. "So I think the African-American community nationwide knows who I am. I'm not saying the others aren't qualified, I'm just saying I've been there."

Biden has maintained relationships with influential Democrats in all of the early-voting states. In Iowa, state lawmakers who introduced him at separate events told stories about him calling to check on their sick children. After his weekend trip to the state, the Biden campaign rolled out endorsements from 23 "key South Carolina lawmakers and political and community leaders," a list that includes six current state lawmakers.

But his ties to South Carolina run deepest. Biden and his wife Jill Biden have vacationed on Kiawah Island, and Biden recently visited Charleston to eulogize former Sen. Fritz Hollings.

Jill Biden told the crowd in Columbia that "South Carolina is a part of us" as she introduced the former vice president at Saturday's rally.

"There's strength in familiarity -- and not just name ID, but real familiarity with him and his record," Columbia Mayor Steve Benjamin, who has not endorsed a candidate, said of Biden in an interview.

He said Biden has "just nurtured strong personal relationships" in South Carolina for decades. Among those, Benjamin said, was former Republican Sen. Strom Thurmond, a segregationist who opposed the Civil Rights Act and died in 2003. But Benjamin said that relationship is "not a liability" at this stage -- though Biden's first visit to South Carolina of the 2020 race featured just a rally, fundraiser and church visit, with little opportunity for the more controversial elements of his record to surface.

Biden's go-to talking point, meanwhile, is that he was Obama's vice president.

He has peppered all of his speeches with references to Obama, often calling him "Barack" or "my buddy" -- a phrase he used Saturday before stopping himself, seemingly to emphasize the reference.

"I shouldn't be so casual. The president of the United States, Barack Obama," Biden said.

But he leaned even harder into their relationship in South Carolina, describing being on hand in Charleston in the wake of the church shooting there when Obama sang "Amazing Grace."

"I watched my buddy Barack stand up there. I watched him talk and he talked about, we have to find that amazing grace," Biden said. "Well by the way, there is amazing grace in this country, we just have to reach out and pull it in."

Biden has also focused in recent days on Republican state efforts to impose strict voting laws.

"We have Jim Crow sneaking back in," he told the crowd in Columbia.

Biden has so far deflected opportunities to draw contrasts with other Democratic candidates -- even Sanders, who has been most aggressive in attacking the former vice president's record.

"I'm not going to speak ill of any Democrat during this campaign, unlike some other Democrats now. That's not useful," he told Columbia's WIS-TV in an interview. "The last thing the Democratic Party has to do is get into a big fight. That only benefits Donald Trump."

Instead, he says he is focused on Trump -- who he called a "clown" at a fundraiser hosted by state Sen. Dick Harpootlian, a long-time Biden ally, on Saturday night in Columbia.

At a farmers' market in downtown Columbia on Saturday morning, Democratic voters said Biden's ability to defeat Trump and his relationship with Obama were both key.

"He's the one that's probably going to be able to beat Trump out of all the other candidates," said Yolanda Mills, who works at an insurance company. "I think because of his experience under Obama that he'll be able to continue on kind of like what Obama started."

"I think someone that truly can beat Trump is what we really need," said Renita Goudelock, an insurance claims adjuster.

She also said older black Democrats are likely to back Biden because of his time as Obama's vice president. "I would say in the black community, they are more prone to people that they're familiar with," she said.

Liz Anderson-Jones, who works in finance, said she is considering Biden and Booker. Biden appeals, she said, "because he was in the Obama administration and I'm an Obama supporter, so he kind of knows what was going on at that point."