In the U.S. Senate campaign debate in Shreveport last week, Democrat Mary Landrieu said she supports increasing the federal minimum wage, while Republicans Bill Cassidy and Rob Maness said they are against it — all somewhat predictably.

Also predictably, Landrieu generally endorses the Affordable Care Act, which she voted for in the Senate, while Cassidy and Maness strongly oppose it.

Less predictably, Cassidy said in the debate that he’s OK with the legalization of medical marijuana, while Landrieu and Maness disagreed with him on that.

They weren’t asked, but all three favor completion of the Keystone XL pipeline to bring tar-sands oil from Canada to the Texas Gulf Coast, though they’ve squabbled over Landrieu’s efforts to push that proposal through a hostile U.S. Senate.

For three candidates from varying points on the ideological spectrum and from strikingly different political backgrounds — Landrieu is a longtime politician, politics is Cassidy’s second career and Maness is a political newbie — the shifting patterns of agreement and dispute might be expected. But while issues play a role in the campaign, they are not at the heart of it.

Landrieu, Cassidy and Maness are not the only candidates in the Nov. 4 election to the Senate from Louisiana — there are five more — but they are the only ones running multimillion-dollar campaigns, and the only candidates making their marks in the opinion polls. If no candidate wins a majority Nov. 4, the top two finishers meet in a Dec. 6 runoff — and the polls indicate there will be a runoff, and that it will match Landrieu and Cassidy.

The election is the focus of national attention — and of millions in outside spending by political groups on different sides — because Landrieu stands as a primary target of the Republicans in their drive to capture the six seats they need for a Senate majority: She’s an incumbent Democrat, and the last remaining member of her party to be elected statewide in an increasingly red state.

In this election, says Charlie Cook, the Shreveport native whose Cook Political Report in Washington covers national politics, “There are only two things that matter: Do people want a Democrat or a Republican in the Senate? And No. 2, who could do more for Louisiana?”

Cassidy hopes the voters focus more on the first question. Landrieu hopes they focus more on the second. Maness hopes they’re sick of Washington politicians of any stripe.

“This is not about me. It’s not about me,” Cassidy has repeated in speeches as well as news outlets local and national. “The president’s agenda is on the ballot.”

Even when Democrat Barack Obama was elected president in 2008 and 2012, he never got more than 40 percent of the vote in Louisiana, and his popularity has dipped below that as his approval ratings nationwide have declined. Republican candidates across the country are seeking to tie their Democratic opponents to Obama, and Cassidy wants to turn the election into a referendum on the president and, by extension, Landrieu.

“She represents Barack Obama. I represent you,” Cassidy said in the debate. “Do you want Sen. Landrieu to complete Barack Obama’s agenda?”

Landrieu pushed back. “While President Obama is not on the ballot, the future of Louisiana is,” she said.

Obama’s second and final terms ends in January 2017. Whoever is elected senator in the fall will keep the job for four years after that, and will spend the bulk of the term serving under a different president.

If that winner is Landrieu, that will extend her Senate tenure to 24 years. She first went to Washington in 1997 — and, as her opponents point out, effectively relocated there with her husband and the first of her two children, moving a few years later to the custom-built house near the Capitol that the couple still lives in.

A victory for Landrieu, 58, also would sustain a remarkable run in elective office that has lasted virtually her entire adult life and a close association with politics that goes back further still. Her father, Moon Landrieu, served eight years as mayor of New Orleans while she was in high school and college. Two years after she graduated from LSU, she was elected to the state House, beginning a nearly uninterrupted stretch as a legislator, state treasurer and U.S. Senator.

It’s her seniority in the Senate that gives Landrieu what she frequently refers to as “clout,” by which she means her ability to exercise influence of behalf of Louisiana. Specifically, that tenure landed her the chairmanship of the Senate Energy and Natural Resources Committee early this year when a longer-serving member left the Senate. As chairwoman of the committee, she holds considerable power over issues dear to the oil and gas industry, which is central to the Louisiana economy and whose interests she has long advanced. But as Keystone shows — and again, as her opponents point out — that influence extends only so far in a Senate controlled by Democrats less friendly to oil and gas than she.

Maybe because of her upbringing, Landrieu comes across as the consummate political animal. She’s comfortable with all kinds of people and relishes the press-the-flesh aspects of politics, as demonstrated this year by her keg-stand assist at an LSU tailgating party and her bust-a-move “wobble” dance at a Southern University tailgate. Although she never forgets her place in the spotlight, she also can sound forthright and unrehearsed.

“She’s a girl who’s from New Orleans,” said Marshall Hevron, a lawyer in the city who worked on Landrieu’s staff in Washington and Louisiana in 2001-06. “If she has an unscripted moment, that’s who she is.

“She’s a hard-charger,” Hevron said. “She’s really committed to getting the work done, but she’s got” — he struggled for the word — “finesse.” By that, he meant, “She really knows how to work with other people.”

Hevron remembers trudging with Landrieu across Cameron Parish in the aftermath of Hurricane Rita, touring devastated communities and meeting with local officials.

“It had just been the longest day,” he said. “She just really wanted to keep on going. Her whole staff was tired, and she said, ‘There’s more people we’ve got to meet with.’ ”

Landrieu has admitted during the campaign to a “temper.” In Hevron’s words, “She can certainly be spirited at times.”

Landrieu ranks as one of the most conservative Democrats in the U.S. Senate, according to the American Conservative Union, based on Senate votes. She scores low among her Democratic colleagues in the environmental ratings of the League of Conservation Voters, due in part to her unstinting support of the energy industry. She draws tepid scores from gun-rights and tough-on-immigration groups, but high marks from organizations focused on seniors, veterans and women.

Cassidy, 57, switched to politics in middle age, winning election to the state Senate as a Republican from Baton Rouge in 2006 after building a successful career as a physician specializing in diseases of the liver at the Earl K. Long charity hospital. He had previously contributed to both Republican and Democratic candidates, including Landrieu in her 2002 Senate run.

Hurricane Katrina prompted his entry into politics, he has said, as he felt a need for improved public leadership in response to the storm. Cassidy’s own response included organizing volunteers to staff a free basic-health clinic for Katrina refugees in an abandoned K-Mart in a low-income neighborhood of north Baton Rouge; earlier, he had helped start a free community clinic for uninsured residents of Baton Rouge, and he also worked to organize a nonprofit program to vaccinate public-school students in the city for flu and hepatitis.

In a one-on-one setting, Cassidy can display personal warmth and a lively intelligence, but in public, he can seem starchy and somewhat awkward; he has not mastered the sound bite, even when set up for one. But he also has an emotional side, almost to a fault: In a recent congressional hearing on dyslexia, he twice broke down in tears while talking about his dyslexic daughter.

“He’s genuine,” said Tom Greene, a veterinarian and former state senator who worships with Cassidy at the Chapel on the Campus, an evangelical Protestant congregation a short stroll from the Cassidy home. “He’s not just going to tell you what you want to hear.

“He votes with his heart,” Greene said. “He’s a man of God and he applies biblical principles to what’s before him. He looks for godly wisdom and he applies it.”

That guidance has led to a more conservative ACU rating for Cassidy than the average House Republican, but not the most conservative among Louisiana House members. He scores very well with gun-rights groups and quite well — though middling among Republicans — with tough-on-immigration organizations. Veterans’ groups like him; seniors organizations, environmentalists and most women’s groups, not so much.

Any account of Cassidy’s political career must include his wife, Laura Layden. A successful surgeon who has retired from medicine and started a charter school for dyslexic students in Baton Rouge, she managed her husband’s first campaign for Congress and by all accounts remains actively engaged in his approach to public life.

As a newcomer to politics, Maness, 52, lacks a political record and interest-group ratings of his positions. But he has embraced the tea party label and the endorsement of Sarah Palin, and his website declares his firm opposition to taxes, the Affordable Care Act, known as “Obamacare,” the Common Core state standards in education and the federal Education Department, amnesty for immigrants, abortion in most cases, gun control, the Veterans Affairs health system, and government regulations and intrusion in general. He calls himself the true conservative in the race and attacks both Landrieu and Cassidy as creatures of Washington. He promises straight talk and defense of the Constitution, except for the clause granting citizenship to anyone born in the United States.

Maness was an Air Force brat who lived in several different states and abroad as a child. He enlisted in the Air Force right out of high school in Tennessee and stayed in for 32 years, retiring as a colonel in 2011. His last post was as commander of Kirtland Air Force Base in New Mexico.

“I found him to be a very strong leader,” said Terri Cole, president of the Greater Albuquerque Chamber of Commerce, on which Maness served as an ex officio member by virtue of his Kirtland command. “He leads with both his heart and his fist.”

Cole described Maness as extroverted, energetic and expressive. She’s not surprised he’s running for office.

“Our country needs strong, compassionate leaders,” she said. “He fits the bill.”

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