Democratic Sen. Mary L. Landrieu and GOP Rep. Bill Cassidy are facing off in one last legislative duel in which the completion of the Keystone XL pipeline is portrayed as so overriding an issue that it will drive votes at the Louisiana polls. Keystone has become important enough to grab a top spot on the agenda of the lame-duck Congress.

But it’s difficult to find proof that Keystone will motivate voters in the state’s runoff election on Dec. 6, or that the last-ditch vote in the Senate expected next week will rescue Landrieu’s campaign to save her seat.

Oliver Houck, a Tulane University law professor who works on coastal restoration issues in Louisiana, said the only visibility Keystone has in the state is among professionals in the energy sector.

“Viscerally, for the people of Louisiana, XL means nothing,” he said.

Keystone is a familiar game for Landrieu and Cassidy, each of whom has tried to demonstrate an ability to pass bills benefiting the state and its energy sector. But on Landrieu’s part, it’s a fourth-quarter gamble that Louisianans will give her credit for finally getting an up-or-down vote on Keystone — and will consider the pipeline a deciding issue for their votes.

Landrieu aides said the Senate Keystone vote is intended to showcase the senator at her best as a legislator who can find opportunities to pass her priorities even in the face of organized opposition. Landrieu would likely become even more influential in a Republican-led Senate, they said, even though she will lose the helm of the Senate Energy Committee when Republicans take control.

Aides pointed to the incoming majority that will still be several votes shy of a filibuster-proof majority and said GOP leadership will likely need moderate Democrats like Landrieu to advance legislation, especially on energy.

But many of the legislative victories Landrieu plays up on the campaign trail, such as the flood insurance premium hike delay and billions in aid money after Hurricane Katrina, directly impacted her constituents, many of whom live on floodplains and lost their homes during the 2005 storm. The tangible benefits to Louisiana if Keystone is built aren’t as firm.

There is the economic impact. The Keystone XL pipeline could indirectly support, and possibly create, jobs on the Gulf Coast by ensuring a steady supply of heavy Canadian crude that refiners there are set up to process. But of the more than 42,000 jobs the State Department has estimated that the project could create, it has pegged 3,900 of those as direct construction jobs in the northern Plains states.

Nonetheless if the northern portion of the Keystone pipeline is built, the Gulf Coast oil industry will likely see a host of job and investment opportunities with the new supply coming down the pipeline, said Louis Finkel, a former Democratic Hill aide who is now executive vice president at the American Petroleum Institute.

“I have to imagine that anything that promotes greater energy production, greater energy development is a boon to a state like Louisiana and is in a lot of ways directly tied to their economic growth,” he said.

However, Bob Mann, a longtime aide to former Sen. John Breaux, D-La., said he doesn’t think Landrieu’s work on Keystone has done much to move the needle among Louisiana voters who aren’t big players in the oil industry. He said he thinks Landrieu emphasizing her clout on energy policy reminds average voters in the state that she’s a “creature of Washington.”

“It has not helped her,” Mann said.

If the Senate passes the Keystone bill ( S 2280 ) sponsored by Landrieu and Sen. John Hoeven , R-N.D.,  Cassidy’s measure ( HR 5682 ) will be considered passed, clearing his legislation for the president. Cassidy may end up getting his name on the legislation, a Landrieu aide said, “but I think Landrieu owns the issue.”

While Landrieu is touting her work on Keystone as an example of her policymaking skills, Cassidy and Senate Republicans hope to convince voters that Democrats are playing politics with the pipeline. GOP senators urged President Barack Obama to issue a statement of administration policy Thursday on the Keystone legislation, daring him to make a formal veto threat against an effort championed by an endangered Democrat.

“It is easy to wonder if the Senate is only considering this because of politics, even so, I hope the Senate and the President do the right thing and pass this legislation creating thousands of jobs,” Cassidy said Nov. 12.

Yet the benefit to Landrieu of getting a vote now as opposed to before Nov. 4 may be very small, said Clancy DuBos, a Louisiana political analyst and columnist. An earlier vote would have undercut Cassidy’s argument on the campaign trail that Landrieu is ineffective as chairwoman of the Senate Energy and Natural Resources Committee since Democratic leadership has avoided bringing energy bills to the floor, he said.

“I do think that if she’d been able to do this eight weeks ago … it would have played very well in Louisiana,” DuBos said.