With the last act of the 2014 U.S. Senate campaign in Louisiana just days away, both Democrats and Republicans are tightening their focus on getting their voters to the polls Saturday for the runoff election.

Opinion polls show Republican U.S. Rep. Bill Cassidy, of Baton Rouge, with a double-digit lead, so the task is especially critical for Democrat Mary Landrieu if she hopes to win a fourth term.

“The odds are daunting,” said political scientist Albert Samuels, of Southern University in Baton Rouge. “It’s obviously going to be turnout, turnout, turnout.”

Landrieu edged Cassidy in the Nov. 4 open primary, 42 percent to 41 percent, leaving both short of the majority needed to win outright and sending them to the runoff. But the combined total for Republican candidates on the primary ballot totaled 56 percent, which is close to the level registered by Republican presidential candidates in 2008 and 2012 in a state turning increasingly red.

If the runoff voters break along similar partisan lines as the primary electorate did, and if Cassidy unifies Republican support behind him, he will win easily.

For Cassidy, that mainly means attracting the support of the primary voters who backed tea-party Republican Rob Maness, who drew 14 percent of the Nov. 4 total.

“Getting out the Maness voters is going to be huge,” said Pearson Cross, who teaches political science at the University of Louisiana at Lafayette. “If you’re Bill Cassidy, you’re nine points away from 50 percent. You’re really thinking, ‘How am I going to reach out to those voters and make the case?’ ”

Cassidy received Maness’ endorsement a few days after the primary, and Cassidy has campaigned with Maness at his side. Tea-party icons Sarah Palin, U.S. Sen. Rand Paul, of Kentucky, and Phil Robertson of “Duck Dynasty” fame also have urged voters to turn out for Cassidy in appearances in Louisiana. More mainstream Republicans such as U.S. Sen. Marco Rubio, of Florida, also have come to the state to recruit voters to Cassidy.

“The one thing we wanted to guard against was voter apathy,” state Republican Party Chairman Jason Doré said.

But Republicans remain committed to winning the election, Doré said.

“They’re still motivated to go out and vote,” he said. “If anything, it’s the Democrats that are less motivated.”

As evidence, Doré points to the results of early voting, conducted from Nov. 22 to Nov. 29. More registered Republicans voted then compared to the early-voting period before the primary, while the number of Democratic early voters declined significantly.

An even steeper decline reduced the early-voting participation of African-Americans, a key constituency for Landrieu that gives her its near-unanimous support.

Cory Booker, of New Jersey, who is the only black Democrat in the U.S. Senate, came to Louisiana to campaign for Landrieu, as did celebrated black musician Stevie Wonder. Recently, U.S. Rep. Cedric Richmond, of New Orleans, a black Democrat, recorded a radio commercial for Landrieu invoking Republican attacks on President Barack Obama, the first black to hold that office, and said a Cassidy victory would mean impeachment. And Obama himself endorsed Landrieu on Monday, although Cassidy has based his campaign on yoking Landrieu to the unpopular president, and she has been less than fervent in embracing him.

Landrieu has staged several campaign events keyed to women to rally another traditionally Democratic voter group. Hillary Clinton, former first lady and secretary of state and leading presidential contender, has campaigned for Landrieu, as has her husband, former President Bill Clinton. But white Democrats such as the Clintons are a disappearing species in Louisiana: Landrieu drew only 18 percent of the white vote Nov. 4, according to exit polls.

White citizens who vote Democratic are thin on the ground across the South, which contributed to the Republican success in capturing control of the Senate by virtue of victories in other states Nov. 4. Democrats hope, however fondly, that with the big prize won, Republicans will stay home or go deer hunting Dec. 6. But the red tide has produced a pro-Cassidy effect, Doré said: Hundreds of paid Republican election field workers, fresh off Senate wins in other states, have poured into Louisiana to knock on doors and urge the Republican voters of Nov. 4 to return to the polls Saturday. Volunteer ranks also have swelled, he said.

“I don’t think the state’s ever seen a deployment quite like this,” Doré said — certainly not on the Republican side. “Everybody knows it’s game day on Saturday.”

The Democrats, too, mounted a major turnout operation before the primary. Kirstin Alvanitakis, a spokeswoman for the state Democratic Party, said a few paid managers have moved on since then, but the Democrats’ paid field force is intact (although the 3-to-1 numerical advantage it enjoyed before Nov. 4 over the paid Republican staff, which numbered in the dozens, has been obliterated by the post-primary Republican influx). Volunteer participation for Landrieu is up, Alvanitakis said.

“We’re going to be adequately resourced to execute our ground game the rest of this week and Saturday,” she said. “We’re convinced we’re going to turn out our voters on Saturday.”

The day of the week should help, in contrast to the primary date on a Tuesday, she said: “We’re a party full of people who are working people.”

Turnout overall in a runoff historically is smaller than in an open primary, and the declines are steeper among traditionally Democratic constituencies, said political scientist Joshua Stockley, of the University of Louisiana at Monroe. Landrieu successfully bucked that trend in 2002 when a strong black turnout helped her score a runoff victory over Republican Suzanne Haik Terrell, but the state was far more blue then than now.

“Sen. Landrieu has a lot more work to do than Rep. Cassidy,” Stockley said. “In many ways, Rep. Cassidy has a natural, built-in advantage with this runoff.”

Follow Gregory Roberts on Twitter, @GregRobertsDC. For more coverage of government and politics, follow The Advocate Politics Blog at http://blogs.theadvocate.com/politics blog.