While the leading candidates in Louisiana’s U.S. Senate race debated on a stage in Shreveport and on TVs throughout the state last week, their Twitter feeds battled it out online.

“Senator Landrieu is clearly desperate. My bill in the state Senate was voluntary and market-based, unlike #Obamacare,” Republican U.S. Rep. Bill Cassidy’s campaign blasted out about 18 minutes into the debate — just one of many tweets that aimed to provide background or spin the candidates’ real-world comments.

“FACT: When @BillCassidy voted for higher taxes on everyone, Mary voted to cut taxes for 99% of Americans,” the Twitter feed for incumbent U.S. Sen. Mary Landrieu, a Democrat, fired off in another of the dozens of debate tweets that night.

The fighting in Louisiana’s hotly contested and closely watched Nov. 4 election wouldn’t be restricted to Centenary College’s auditorium that night, and the Web-based, behind-the-scenes war illustrated just how important social media and other online tools have become for campaigns.

“We have to go to the voters; we don’t wait for voters to come to us,” said Kirstin Alvanitakis, spokeswoman for the state Democratic Party and a prolific tweeter. “Increasingly, where people are is on social media.”

Cassidy’s campaign posts countless photos on Facebook — pictures of the Baton Rouge congressman playing beach volleyball, making burritos at a Baton Rouge Qdoba fast-food restaurant, shaking supporters’ hands.

John Cummins, a Cassidy campaign spokesman, said social media have become an important tool in the election, which likely will be decided between Cassidy and Landrieu in a Dec. 6 runoff.

“We use it to let folks know where Dr. Cassidy visits, where he stands on important issues and also to interact with Louisianans,” he said. “It has allowed us to spread Dr. Cassidy’s message to every corner of the state.”

According to Landrieu’s campaign, the senator often suggests or dictates posts to Twitter and Facebook. She said she recognizes the role social media play in campaigns these days, particularly when compared with her last election.

“When I last ran in 2008, I owned a flip phone that didn’t even have a camera on it. iPads weren’t invented. Instagram didn’t exist,” Landrieu said. “Now, most people own a smartphone, are glued to Facebook and are tweeting up a storm.”

Retired Air Force Col. Rob Maness, a tea party-backed Republican and the third leading candidate in the race, also has made use of social media to gain political traction. His campaign regularly responds directly to supporters, posts photos of him at events and promotes radio and television appearances through his Facebook and Twitter feeds.

The campaigns this cycle have used Facebook and Twitter to ask for campaign contributions, to promote events and to respond directly to their critics and supporters.

Over the weekend, Landrieu’s campaign sent out nearly a dozen tweets promoting former President Bill Clinton’s scheduled appearance at a Landrieu rally on Monday.

Cassidy, who worked as a doctor before entering politics, regularly strikes out against the federal Affordable Care Act and recently has taken to criticizing President Barack Obama’s response to the Ebola virus outbreak.

During the debate, observers quickly were able to pick apart talking points and report their judgments of the candidates with rapid-fire responses of their own online.

For all of the candidates, the online sphere provides a way to try to reach younger voters and those who work at computers. And the free medium offers an interactive element that isn’t available through television and other traditional campaign tactics.

Landrieu’s campaign slogan “I’m with Mary,” which appears on her campaign signs, was quickly converted to a hashtag that has been used frequently by supporters.

Republicans also seized on the potential for social media this year with a voter challenge modeled after the popular “ice bucket challenge” that benefited the fight against Lou Gehrig’s disease and took social media by storm this summer.

The idea: GOP voters go online, pledge to vote, post to their Facebook pages and challenge friends to do the same.

“We’re really trying to attract as many voters to our candidates and our party as possible,” said Ben Voelkel, a Republican National Committee spokesman based in Louisiana. “Social media is just another great way to reach them.”

Meanwhile, Landrieu has seen the ripple effects of social media that are beyond her direct control. In recent weeks, a photo of her assisting an LSU fan with a “kegstand” during pregame tailgating and a video of her doing the popular dance the “Wobble” at a Southern University tailgate have gone viral, thanks to Twitter and Facebook.

Follow Elizabeth Crisp on Twitter, @elizabethcrisp. For more coverage of Louisiana politics, follow our Politics blog at http://blogs. theadvocate.com/politicsblog.