At 11 o’clock of the morning after, U.S. Sen. Mary Landrieu was up and at ’em, attacking her runoff election opponent, Bill Cassidy, at a news conference Wednesday at the construction site of the billion-dollar Veterans Affairs medical complex in New Orleans.

Cassidy, she said, had opposed the project when he served in the state Senate. But she supported the ambitious plan to replace the old VA hospital taken out by Hurricane Katrina in 2005.

“Where was Bill Cassidy when the decision to build this hospital was being made?” she asked, flanked by supporters holding placards showing a caricature of Cassidy and the phrase, “Where was Bill?”

“This is the time for Bill Cassidy to stand up and talk about his own pitiful record.”

Cassidy, apparently, disagrees: He scheduled no public appearances Wednesday, the day after he finished a close second to Landrieu in the open primary. With neither he nor Landrieu capturing the majority that would provide an outright victory in the primary, the two will square off Dec. 6.

There’s a reason for Cassidy to be confident: The picture painted by the returns Tuesday is not a pretty one for Landrieu.

“This was obviously the outcome that the Cassidy camp hoped for,” said Bryan Brox, who teaches political science at Tulane University. “They made the runoff. That’s all they needed to do.

“The turnout in December is going to be a lot lower, and they no longer have to face that additional conservative on the ballot.”

That additional conservative is Rob Maness, the tea party Republican who finished third in the primary, with 14 percent of the vote. He ran to the right of Cassidy, a Baton Rouge congressman endorsed by the Republican establishment (and rated as more conservative than the average House Republican).

Cassidy won 41 percent of the primary vote, just behind Landrieu’s 42 percent. Now Cassidy is the lone Republican on the ballot, set against a three-term Democratic incumbent who lost a combined 56 percent of the vote to Republican challengers (a minor Republican candidate took 1 percent). And although Landrieu scores as one of the least liberal Democrats in the Senate, Cassidy is much closer to Maness on the political spectrum than she is.

Landrieu, then, is trying to change the frame of the election. The Republican tide that’s been rising in Louisiana for years — Landrieu’s 2008 Senate campaign was the last time a Democrat won a statewide election in Louisiana — flooded the country Tuesday, giving Republicans a Senate majority to add to their control of the U.S. House.

“The national race is over,” Landrieu said Wednesday. “This race is about who’s going to represent the 64 parishes.”

But the Republicans’ success in the other Senate elections Tuesday devalues one of the strongest cards Landrieu had to play: As a senior member of the Democratic majority, she took over this year as chairwoman of the U.S. Senate Energy and Natural Resources Committee, with oversight of the oil and gas industry central to the Louisiana economy. Win or lose Dec. 6, Landrieu will relinquish her chair to a member of the Republican majority in the new Congress in January.

Nonetheless, Landrieu said Wednesday, “I’m prepared to run on my record of delivering for the state.” And she wants to highlight the contrast with what she called the “pitiful record” of her “wishy-washy, unreliable, irresponsible” opponent.

Her combative tone was similar to the one she struck election night in a speech to her supporters after the results came in.

“She was fired up, she was animated, she threw the gloves off,” said Joshua Stockley, a political science professor at the University of Louisiana at Monroe. “She’s clearly not going to go down without a fight.”

Cassidy, though, has not shown much eagerness to grapple with her. He agreed to participate in just two televised debates before the primary, leaving Landrieu and Maness to argue with one another in two others (Landrieu has upped the ante for the runoff, challenging Cassidy to no fewer than six debates).

Nor has Cassidy slugged it out toe-to-toe with Landrieu on the issues. Instead, like a broken jukebox, he’s played the same song over and over: Landrieu has supported Democratic President Barack Obama 97 percent of the time. That’s pretty much the same tune sung by Republicans everywhere, as they capitalized Tuesday on deep and widespread disaffection with the president.

“Cassidy, to his credit, for the last month, the only thing he talked about was that Landrieu voted with Obama 97 percent of the time,” Stockley said. “She’s got to take that off the table.”

Cassidy won’t change his game plan, said Albert Samuels, who is on the political science faculty at Southern University.

“Cassidy is going to do what he’s been doing,” Samuels said. “He’s taking on an anti-Obama sentiment. He also hopes to draw in a lot of voters who favored Rob Maness.”

Landrieu’s biggest challenge may be one that baffled her campaign in the primary: getting her supporters to take part in the election. It’s a task that proved daunting to Democrats across the country.

Despite a sophisticated $60 million nationwide effort to get out their vote, the Democrats achieved little success in overcoming the tendency for many of their traditional constituencies — minorities, young voters, lower-income voters — to sit out elections that don’t include a presidential race. Voter turnout in Louisiana on Tuesday barely exceeded 50 percent — not much better than the turnout in 2010, and well short of the participation rates of 2008 and 2012.

“It starts with turnout,” Stockley said. “What we saw in Louisiana and across the nation last night were core Democratic constituencies under-voting.”

Making things even worse for Landrieu, Stockley said, is that the number of voters participating tends to shrink even further in a December runoff.

“The further removed you are from the presidency, and the further removed you are from headline elections, the narrower the electorate is,” Stockley said.

And that smaller voter pool typically includes a disproportionately high percentage of “your older voters, your wealthier voters — those are electorates that favor, at this time, Rep. Cassidy,” he said.

“The odds are daunting,” Samuels said. “It’s obviously going to be turnout, turnout, turnout.”

Landrieu, though, has faced adversity before, and overcome it.

In her first Senate election, in 1996, Landrieu ran second in a 15-candidate primary field to Republican Woody Jenkins, and the combined Republican vote was 56 percent of the total; she beat Jenkins in the runoff by 5,788 votes — a margin, as she likes to point out, of fewer that 11/2 votes per precinct. In 2002, the combined Republican vote in the primary again was more than half the total, although Landrieu easily finished first and beat Republican Suzanne Haik Terrell 52-48 in the runoff. Only in 2008 did she win outright in the primary.

“Mary’s the kind of candidate, she’s always been a scrappy candidate,” Samuels said. “She’s won some very close races. It’s difficult, given her past history, to just write her off and say she’s doomed.

“But I do believe this is the toughest race she’s ever had.”

Follow Gregory Roberts of The Advocate Washington bureau on Twitter, @GregRobertsDC.