The suspense around today’s scheduled Senate vote on the Keystone XL pipeline isn’t over whether the controversial proposed 1,100-mile conduit for carrying the product of Canadian oil sands to Texas refineries. That, after all, will be up to President Barack Obama, since Keystone XL supporters don’t have the votes to override a veto.

And it isn’t about who will control the Senate: Whether Louisiana Sen. Mary Landrieu, the pro-oil business Democrat who engineered the attempt to force Obama’s hand on Keystone to save her own seat, wins or loses in her state’s Dec. 4 runoff, Republican Sen. Mitch McConnell of Kentucky becomes majority leader a month later.

No, the real intrigue is the competition among the deep-pocketed special interests arrayed on both sides of the debate, all of whom have the potential to entice — or threaten — senators planning to run for re-election in the future.

A handful of centrist Democrats will determine whether the Keystone measure will land on Obama’s desk.

One who recently announced his support for the Landrieu bill calling for the pipeline to be green-lit is Democratic Sen. Michael Bennet of Colorado, who is up for re-election in 2016 and just saw nouveau super PAC investor Tom Steyer, who has made reducing carbon emissions a rallying cry, spend $7.2 million in his state in a failed effort to get Democratic Sen. Mark Udall re-elected. Perhaps coincidentally, Bennet last year received two contributions of $1,000 each from the lobbying firm that has been representing Saskatchewan, the Canadian province doing much of the lobbying for Keystone XL.

Steyer, meanwhile, became the year’s largest donor to super PACs, spending $73 million, in his effort to support candidates sympathetic to his views on climate change. His return on investment, however, was a less-than-impressive 32 percent. Even so, Steyer promised to keep hitting “climate deniers” in 2016.

The League of Conservation Voters (LCV) had similar luck this year, but it wasn’t for want of effort. The green group spent at least $17.5 million on elections through its super PAC and dark money operations. The North Carolina Senate battle was its biggest investment at more than $5 million. But the LCV’s two arms spent almost $3 million in Colorado against Republican Cory Gardner.

On the other side of the Keystone XL debate are another set of major political players.

The American Petroleum Institute (API), to take one example, is a prolific campaign donor (Landrieu has been their top recipient) and a savvy player of the grassroots influence game.

API has been pressuring on the fence legislators to approve the pipeline with a series of national TV ads, like this one urging viewers in Delaware to “Tell Senators Coons and Carper: approve Keystone XL.” Sen. Tom Carper, the state’s senior Democratic senator, already announced his support for Landrieu’s measure greenlighting the pipeline. The Hill reports that his fellow Delaware Democrat, Sen. Chris Coons, remains on the fence, along with Sen. Angus King, I-Maine.

Recently, building trades unions have chartered unfamiliar territory in support of the pipeline. Laborers’ unions gave hundreds of thousands of dollars to a super PAC dedicated to electing centrist candidates. That PAC, Defending Main Street, spent nearly $500,000 to re-elect Republican Congressman Mike Simpson of Idaho, a chief agitator for construction of the oil pipeline.

LIUNA, the Laborers’ International Union, recently upped its campaign profile, launching a new super PAC in September and dishing out $475,000 to the Democratic House Majority PAC.

Lobbyists for Canadian interests behind the pipeline have also been active givers to key voting blocs.

South Dakota Sen. Heidi Heitkamp, for example, a Democrat who’s in favor of the pipeline, met with lobbyists from lobbying firm Nelson Mullins and got a $1,000 campaign contribution in April. The South Carolina-based lobbying shop has reported more than $4 million in income this year for its efforts to influence Congress for a wide ranging list of clients, including the Canadian oil provinces of Alberta and Saskatchewan, the International Music Products Association and the auto equipment maker TRW, according to OpenSecrets.org and Foreign Influence Explorer. Its political largesse has extended to dozens of state and federal candidates.

Saskatchewan is just one facet of an inside battle that has tilted decidedly in Keystone’s favor. Pro-pipeline groups have dominated the inside game, far outpacing anti-pipeline activists in both lobbying expenses and active lobbyists.

A Sunlight Foundation study earlier this year, found that 10 of the top 12 groups lobbying on Keystone were in support of the pipeline, including each of the top five.

Obama has been lukewarm about the project and his signature is dubious. Pro-Keystoners don’t appear to have the two-thirds majority needed to override a presidential veto.

Even if the latest pipeline push stalls, however, it isn’t likely to put a halt to the multimillion dollar influence battle that’s raged on and off Capitol Hill for the past six years.

Ironically, one place it’s not raging is Louisiana.

If the Senate iteration of the pro-Keystone bill clears the 60 vote cloture threshold — a vote is scheduled Tuesday — it will be thanks in large part to the efforts of the embattled Landrieu. Her political career is hanging on by a thread as she awaits a runoff election against Republican Rep. Bill Cassidy, who introduced the House bill okaying Keystone. Energy companies have largely stood on the sidelines in that race. Both candidates are close allies and campaign beneficiaries of oil and gas interests.