Democratic incumbent Mary Landrieu and Republican U.S. Rep. Bill Cassidy clashed in an often contentious campaign debate Monday night as they count down the days to the U.S. Senate runoff election Saturday.

Neither candidate stumbled badly or landed a knockout punch, but their exchanges were testier than their confrontations in earlier debates in the long campaign. Landrieu showed a combativeness that is one of her trademarks, but for Cassidy, the intensity of his performance — if still somewhat wonky — contrasted with a previous style that could appear wooden.

Cassidy drummed away at his No. 1 theme: that Landrieu marches in step with her fellow Democrat, President Barack Obama, who is widely unpopular in Louisiana and nationwide.

“Families are struggling, and they’re struggling because of the Obama-Landrieu agenda,” Cassidy said in his closing remarks. “Sen. Landrieu supports Barack Obama 97 percent of the time.

“Sen. Landrieu represents Barack Obama. I represent you.”

In her closing, Landrieu sounded her major theme: that the election represents a clear choice between Cassidy and “a senator that has worked for 18 years, with honesty and with integrity, delivering for every part of this state.”

The debate was the only one of the runoff campaign, which started after the Nov. 4 open primary. Landrieu pressed for more debates, but Cassidy agreed to only one, in keeping with his cautious, risk-avoidance campaign strategy — typical for candidates who feel they hold a winning hand.

Landrieu edged Cassidy in the primary vote, 42 percent to 41 percent, but the combined total for Republican candidates on the ballot totaled 56 percent, and polls consistently have predicted that Cassidy will ride the red wave to an easy victory Saturday. That would give the Republicans a gain of nine Senate seats in the fall elections nationwide and extend their majority to 54 of the 100 senators in the 2015-16 Congress. It also would mean no Democrat would hold a statewide office in Louisiana; Landrieu’s election to her third term, in 2008, was the last time a Democrat won a statewide race.

In the last week, Landrieu has sought to capitalize on Cassidy’s work record as an LSU physician while serving in Congress, arguing that he is collecting taxpayer dollars as pay without demonstrating that he has put in the time to earn them. Cassidy has said his $20,000-a-year salary is not tied to specific time or performance measures (he took an unpaid leave of absence from LSU this spring).

The first question of the debate addressed the controversy but also brought up a money issue that bedeviled Landrieu earlier in the campaign: her use of public funds allocated to her Senate office for charter flights to campaign events, in violation of Senate rules. Landrieu earlier acknowledged the violations and paid back more than $30,000 from her campaign funds, and Monday night repeated her contention the wrongful payments were the result of bookkeeping errors.

Landrieu then went on the attack over the LSU employment issue.

“Congressman Cassidy has padded his own payroll for the last six years,” she said.

Cassidy defended his work as helping the uninsured and the poor.

“When I treat patients in the public hospital system, clearly those patients benefit,” he said. “But when she takes jets on the taxpayer dime to campaign events, who benefits?”

After the debate, Cassidy quickly left WAFB-TV studios but Landrieu stuck around to talk with reporters.

She handed out her flight records from her first term, which Republicans had “demanded” of her, and they showed seven flights from 1999 to 2002, at total cost of $10,216.

She noted that Cassidy failed to bring records supporting the work he claims to have done teaching resident physicians at LSU.

“This is a serious matter,” Landrieu said. “I’m glad LSU is investigating. … The last thing we need is a senator going to the Senate under investigation. We’ve had enough of that.”

The combination of Obama and health care represented in the Affordable Care Act — the president’s signature legislation, passed in 2010 with Landrieu’s support and known as “Obamacare” — emerged as a major point of contention in the debate.

Cassidy said it has forced families to spend more for health coverage they don’t want. He advocates repealing the ACA.

Landrieu said “Obamacare” has made health insurance affordable for many who could not pay for it before.

“This law is not perfect,” she said. “It needs to be fixed, it needs to be improved, but it is better than the system that we had.”

The election is the most expensive Senate race in Louisiana history. Landrieu has taken in more money in direct contributions to her campaign, but outside political groups have spent millions attacking or supporting the candidates — and since the primary, outside spending on Cassidy’s side has dwarfed that favoring Landrieu. Official national Democratic organizations have abandoned Landrieu in the runoff.

Cassidy, 57, is a third-term congressman from Baton Rouge and a physician. He has relentlessly repeated that Landrieu has supported Obama 97 percent of the time in her Senate votes, seeking to associate her with the unpopular president — a tactic adopted by many Republican Senate candidates in other states.

Landrieu, 58, has spent most of her adult life in state and federal elective office. She has played up her ability to work across the partisan divide in delivering federal money to the state. But the Democrats’ loss of Senate control robbed her of one of her main selling points: that she can wield her power as chairwoman of the Senate Energy and Natural Resources Committee to benefit the oil and gas industry that is central to the Louisiana economy. The Republicans will pick the committee chairwoman in the next Congress, and they have promised Cassidy a junior seat on the committee.

Landrieu gambled on demonstrating her clout when she brought a bill to greenlight the Keystone XL pipeline to the Senate floor within days after the open primary. She had long favored the project, which would bring “dirty” oil from the tar sands of Canada to refineries on the Texas Gulf Coast, but environmentalists oppose it and the Senate Democratic leadership had blocked its consideration. In the end, Landrieu fell one vote short of the 60 needed for approval.