Recognizing the pivotal role that South Carolina may play in the 2020 race for the White House, Democratic candidates have crisscrossed the state more than a full year before the primary takes place.

Five U.S. senators — Cory Booker, Kamala Harris, Amy Klochubar, Bernie Sanders and Elizabeth Warren — and two others seeking the Democratic presidential nomination, former U.S. Rep. John Delaney and author Marianne Williamson, have traveled to South Carolina in the past two months. Another potential candidate, U.S. Sen. Sherrod Brown, is coming this weekend.

Their early appearances show that the race to win the state's Democratic primary is already "on steroids," said Danielle Vinson, a professor of politics and international affairs at Furman University.

Trav Robertson, chairman of the South Carolina Democratic Party, said stakes will be high in the primary.

"We are going to have an extremely large role in possibly picking the next president of the United States," he said.

Why South Carolina matters so much in the 2020 presidential race

Experts list three factors why candidates are focusing on South Carolina: the timing of the state's primary, the diversity of its Democratic voters and the relatively low cost of campaigning here.

The South Carolina Democratic presidential primary will be held on Feb. 29, 2020. It comes on the heels of the first contests in the race — the Iowa caucuses, the New Hampshire primary and the Nevada caucuses — and just three days before the Super Tuesday primaries in 10 states, including North Carolina, California, Texas and Massachusetts.

The winner of the South Carolina primary will hope that success turns into a "contagion" that spreads across the Super Tuesday states, said Bruce Ransom, a political science professor at Clemson University.

Vinson echoed his assessment, stressing that a victory in South Carolina is a "great way to get momentum."

For candidates who do poorly, however, the Palmetto State may be the end of the line.

"If you're not in a position where you're among the first-tier candidates, your chances of raising money and getting attention are pretty well done," said Charles Bierbauer, who covered five presidential campaigns for CNN before becoming dean of the University of South Carolina's College of Mass Communications and Information Studies, a post he retired from in 2017.

The makeup of the state's Democratic voters also will serve as an opportunity for candidates to illustrate that they have a broad appeal. Unlike in Iowa and New Hampshire, black voters are expected to cast a majority of the votes in South Carolina's Democratic primary.

"We look more like America," Bierbauer said.

And, as Robertson pointed out, "it is cheap to campaign in South Carolina." He cited Klobuchar's visit last weekend, when she was able to meet with voters and gain media coverage in Greenville and Columbia "for the cost of a tank of gas."

The economics of the race will change after the South Carolina primary when candidates will be forced to wage campaigns in multiple states at the same time from March through early June.

"After South Carolina, the map kind of explodes on them," Bierbauer said. "South Carolina is the last inexpensive place to campaign and make a mark. This is the last proving ground before you have to go big."

Seeking votes in the Upstate

While Greenville County and the rest of the Upstate are seen as a Republican stronghold, Warren and Klobuchar held campaign events in Greenville this month that attracted hundreds of people. Delaney spoke at Clemson University on Wednesday night, and Booker will test the waters Friday at a church in Simpsonville.

Even though they may be outnumbered by their GOP counterparts, there are a sizable number Democrats in the Upstate. The 31,398 voters in Greenville County who cast ballots in the state's 2016 Democratic presidential primary marked the third highest total in South Carolina, trailing only Richland and Charleston counties.

Adding in the votes from Anderson and Pickens counties with those from Greenville shows that the three counties accounted for about 12 percent of the total ballots in the state's 2016 Democratic presidential primary. Hillary Clinton won the 2016 primary with 73 percent of the votes, compared to 26 percent for Sanders.

Since the Democratic primary is open to all voters, there also is the possibility that independents and some Republicans who don't support President Donald Trump will decide to cast ballots.

In what will likely be a hard-fought contest, candidates can't afford to overlook any part of the state, Robertson said.

"You have to go to Anderson," he said. "You have to go the Upstate."

Joe Biden, Michael Bloomberg and Beto O'Rourke could alter the race

Democratic voters will have "clear choices" in the primary, Vinson said.

"These candidates are not all the same," she said.

She said Warren, who has proposed a "wealth tax" to pay for universal child care, appears to be the most progressive while Klochubar is seeking to position herself as a moderate with other declared Democratic candidates falling somewhere in between.

The current political landscape could shift if Vice President Joe Biden and other candidates such as former New York City Mayor Michael Bloomberg or former U.S. Rep. Beto O'Rourke of Texas decide to join the race.

National polls and at least one South Carolina survey indicate that Biden would immediately become the Democratic front-runner.

"I believe it is a question of not if but when," said James Smith, a former state representative who lost to Gov. Henry McMaster in last fall's gubernatorial election.

"We need someone who can bring this country together, and I think he is in the best position of any candidate, Republican or Democrat, to be able to do that," Smith said.

While Bierbauer agreed that Biden is a popular political figure, he also said that he has some vulnerabilities.

"He's especially well-known and well-liked among South Carolina Democrats — there are probably even Republicans in South Carolina that like Joe Biden," he said. "But is he too much the old-guard? Is he too old? If the party is moving to the younger generation, Biden is too old and presumably Sanders is too old."

Beirbauer said Bloomberg could shake up the Democratic race partly because he is a billionaire who could mount a campaign without facing any financial constraints.

Vinson sees O'Rourke as a possible wildcard because of his ability to reach out to young people and others who have never taken part in the political process. O'Rourke narrowly lost last fall in his bid to unseat U.S. Sen. Ted Cruz.

Will S.C. primary lead to long-term gains for Democrats in the state?

Anderson County Democratic Party Chairman Mike Kay is counting on next year's primary to help grow the party in his county and throughout the state.

"I think we are going to see a lot of activity," he said. "It is going to be a good year."

Kay said he will be working to line up volunteers for the various Democratic presidential candidates. He then hopes to turn those volunteers into future candidates for seats on the Anderson County Council and other elected posts.

While Republicans maintain a solid grip on the General Assembly and statewide offices, Democrat Joe Cunningham achieved a major win for his party by capturing the state's 1st Congressional District last fall.

Vinson said there are indications that the GOP is out of step with younger voters who are concerned about climate change and support social issues such as gay rights.

She said the 2020 primary "is a great opportunity for people to hear what Democrats are talking about."

Follow Kirk Brown on Twitter @KirkBrown_AIM