Voter turnout is expected to drop off sharply for Tuesday’s primary runoff election for the U.S. Senate.

Election officials estimate about 210,000 eligible voters, or 10 percent of those registered, will go to the polls to pick the Republican nominee — either former Gov. David Beasley or U.S. Rep. Jim DeMint.

Some 293,000 people turned out June 8 to choose from among six candidates in the initial GOP primary. Since no one captured a simple majority, the two top finishers were thrown into a runoff.

The winner will face Democrat Inez Tenenbaum on Nov. 2.

The candidates are seeking the seat being vacated by Democrat Fritz Hollings, who is retiring after 38 years in the U.S. Senate.

“Traditionally, voter turnout is lower in runoff elections,” said Curtis Gans, president of the Washington-based Committee for the Study of the American Electorate. “It’s hard to get voters back out whose candidates lost in the first round.”

Drop-off in voting is usually about 30 percent, experts say, but there are exceptions.

In 2002, some 316,000 people voted in the seven-person Republican gubernatorial primary. More than 305,000 — about 97 percent — returned to participate in the runoff.

S.C. State University political scientist Willie Legette predicts Tuesday’s turnout will be smaller than usual.

“There’s not a big difference between the two candidates on the issues,” he said. “A low turnout will benefit Beasley because he has high name recognition and his supporters feel a greater commitment to him.”

Francis Marion University analyst Neal Thigpen agrees.

“DeMint’s backers could be on vacation in the Bahamas,” he said. “Beasley’s guys are going to come out.”

Turnout will be the key.

“Whoever can get their troops out on election day is going to be the victor,” said Robert Jeffrey, a Wofford College professor. “It’s going to be close.”

Beasley and DeMint are cranking up their get-out-the-vote campaigns to assure a good turnout Tuesday.

DeMint conducted a three-day bus tour across the state over the weekend and planned several meet-and-greets before balloting begins.

In addition, the congressman’s campaign will have volunteers working phone banks, making 4,000 to 5,000 calls a day urging voters to go to the polls on Tuesday, said Terry Sullivan, campaign manager for DeMint.

He estimates a turnout of 275,000.

“We win, whatever the turnout,” Sullivan said.

Beasley plans a last-minute whirlwind tour of the state.

Without revealing their plans, campaign aides said they had an aggressive game plan to turn out their votes, and that will be the difference between winning and losing.

Reach Bandy at (803) 771-8648 or lbandy@thestate.com Staff writer Valerie Bauerlein contributed to this report.