— Chances are that Republican Bill Cassidy doesn’t consult an actual game plan that spells out how he can unseat Democrat Mary Landrieu in the U.S. Senate race in Louisiana that will be decided Dec. 6.

But if he were doing so, it could read something like this:

  • For the Nov. 4 open primary, establish a position as the best-financed, mainstream Republican candidate to fend off any tea party challenge.
  • Hang the albatross of President Barack Obama — a Democrat widely unpopular in Louisiana — around Landrieu’s neck.
  • Finish first or second in the primary while keeping Landrieu below the majority needed for an outright win, to set up a head-to-head, Republican-vs-Democrat showdown with her in the Dec. 6 runoff in a state that increasingly votes Republican.
  • Unify Republicans behind your candidacy in the runoff.
  • Draw lots of support from highly motivated national Republican organizations and conservative political groups for advertising and field operations in runoff.
  • Avoid mistakes. Run a risk-averse campaign.
  • Ride the Republican wave to victory Dec. 6.

So far, so good for Cassidy, who, if opinion polls are to be believed, is well on his way to ending Landrieu’s 18-year run in the Senate.

“I don’t think he needs to do much differently than he did in the primary,” said Jennifer Duffy, a senior editor with the national Cook Political Report in Washington. “He’s done the biggest thing he needed to do, which is unify the party.”

Under Louisiana’s open primary system, all candidates, regardless of party, are listed on the same ballot in November. If no candidate captures a majority of the primary vote, the top two finishers meet in a December runoff.

Cassidy, 57, a three-term congressman from Baton Rouge, wound up as the only Republican with experience in public office listed on the Nov. 4 ballot. But Rob Maness, a retired Air Force colonel who lives in Madisonville, joined the race as a Republican with the backing of national tea party groups.

Maness’ unexpectedly strong campaign won him 14 percent of the primary vote — well short of Landrieu’s 42 percent and Cassidy’s 41 percent but enough to force them into a runoff. Including a third, minor candidate, Republicans in the primary captured a combined 56 percent of the vote.

“For Cassidy, it’s obviously about pulling the party together,” said the Cook Report’s director, Charlie Cook.

Maness managed to carve out ideological space to Cassidy’s right — no easy trick, as Cassidy is rated as more conservative than the average House Republican, based on his voting record in Congress.

“There’s not really much daylight between some of the positions Cassidy has taken and some of the positions the tea party has taken,” said Albert Samuels, a political science professor at Southern University in Baton Rouge.

But Cassidy is certainly not a right-wing firebrand: His political style is relatively low-key and even somewhat starchy.

“The thing about Cassidy is, he’s widely acceptable but not the most preferable for a lot of Republicans in the state,” Cook said “He doesn’t throw red meat and get them enthusiastic. So his strength is also his weakness: He can go after swing voters, but he doesn’t rev up the base.

“In the runoff, he just needs those voters to just see red” — red, as in Republican, Cook said.

It took Maness a few days, but he endorsed Cassidy after the runoff. So did Tony Perkins, the evangelical Christian leader, who previously had supported Maness over Cassidy. Maness appeared at a Republican “unity rally” in Baton Rouge on behalf of Cassidy, as did Louisiana U.S. Sen. David Vitter, Gov. Bobby Jindal and U.S. Sen. Rand Paul, of Kentucky, a tea party favorite. Soon after that, Cassidy was joined by Maness at a campaign stop near Monroe, along with Phil Robertson, the gun-and-Bible-totin’ star of “Duck Dynasty,” and former vice presidential candidate Sarah Palin, a tea party icon who had pointedly endorsed Maness in the primary.

“That’s good for reminding people that there’s an election and reassuring those far-right people that Cassidy is a better alternative than Sen. Landrieu,” said Joshua Stockley, who teaches political science at the University of Louisiana at Monroe. “It certainly doesn’t hurt Rep. Cassidy to have these headlines indicating that all these Republicans are supporting him and endorsing him.

“That average guy who just went out and voted for Maness because he represented the tea party, when they see Maness urging people to vote for Cassidy, yeah, he’s going to respond to that.”

“The big question for Bill Cassidy is, can he get those real conservative north Louisiana voters, and can he get those Christian voters?” said Pearson Cross, a political scientist at the University of Louisiana at Lafayette.

Cassidy need only round up the same share of the vote — 60 percent — received by the Republican presidential candidates in 2008 and 2012 to cruise to victory, Cross said.

“Cassidy just has to run a standard base campaign,” said Brian Brox, a political scientist at Tulane University in New Orleans.

“He needs to lock down white voters and conservatives,” Stockley said. “If he can get 80 to 90 percent of the conservatives to vote for him, if he can get 75 percent of the white voters to vote for him, if he can limit the gender gap to 5 percent or less, he will win.”

Landrieu, 58, has a near-total lock on black voters — she won the support of 94 percent of them in the primary, according to exit polls — but black voters make up only 31 percent of the electorate. Landrieu’s 18 percent of the white vote in the primary is almost certainly too little to win a head-to-head contest with Cassidy.

Landrieu supporters point to other times when she has beaten the odds, as in 2002, when, in her first run for re-election, she fell short of a majority in a primary in which Republican candidates combined for more than half the vote. In the runoff, she beat Republican Suzanne Haik Terrell 52-48.

But that Republican primary vote total in 2002 was a bare majority of 51 percent, and Landrieu’s primary showing that year was 4 percentage points better than what she pulled Nov. 4, as she attracted a considerably larger share of the white vote. Also, Louisiana was not as deeply red as it is now: In 2002, both U.S. senators were Democrats, as were two of the seven House members, the lieutenant governor and the state attorney general. Today in Louisiana, the only Democrats in Congress are Landrieu and Cedric Richmond, from the black-majority 2nd District. And no Democrat has won a statewide vote since Landrieu’s last Senate election in 2008.

The Cassidy campaign can count on two other strengths, Duffy said: money and organization. National Republican organizations are providing cash and field workers on a level the Democrats have yet to indicate they will match. Other outside backing for Cassidy in the runoff, mainly in the form of political advertising by independent, conservative political groups, has run close to $2 million, while Landrieu has received little or nothing.

Cassidy also stands to benefit from two developments beyond his control.

In the general elections in other states Nov. 4, a red wave provided Obama-bashing candidates enough seats for Republicans to take over control of the Senate in the next Congress, meaning Landrieu will lose her position as chairwoman of the Senate Energy and Natural Resources Committee and can no longer promise to use its clout for the benefit of Louisiana’s dominant oil and gas industry.

And after the Nov. 4 voting, Landrieu bucked her fellow Democrats in the lame-duck Senate and tried to push through a bill greenlighting the Keystone XL pipeline — a move of seeming desperation that ended in highly publicized failure.

The biggest threat to the Cassidy campaign may be complacency.

“They can’t take this for granted,” Duffy said. “The Cassidy campaign has to pay real attention to — and communicate to their supporters — why it’s important to turn out, because certainly that is what Landrieu’s doing with her supporters.”

Despite Maness’ endorsement of Cassidy, and despite the much greater distance politically between Maness and Landrieu, there’s no certainty that Maness’ voters will line up behind Cassidy in the runoff — or if they will vote at all.

“Some of them will go to Cassidy,” Stockley said. “I think a proportion of them, and enough of a proportion that could be significant, will sit out in the runoff.

“Rather than compromise by voting Republican-light, they just don’t vote,” he said.

Although it seem paradoxical, Cross said, some Maness supporters may vote for Landrieu in the runoff.

“Voters are not automatons,” he said. “They’re not machines.”

But given Landrieu’s financial disadvantage and her dismal showing among white voters, the Cassidy campaign clearly sits in the driver’s seat, Samuels said.

“It’s their election to lose,” he said.

And Cassidy has played it that way, relentlessly directing the voters’ attention to Landrieu’s Democratic fellowship with the much-maligned Obama instead of grappling with her over big issues and even, incumbent-like, avoiding televised debate appearances with her.

“For the Cassidy campaign,” Samuels said, “essentially, the strategy is, ‘Don’t screw it up.’ ”

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