The trouble with broad analysis pieces on campaign cash is that they often go for eye-popping numbers while obscuring uncomfortable political realities. For example, Greenwire reported this morning that the 27 senators who remain undecided on the chamber’s pending climate bill took "more than $20 million … over the past two decades from energy interests with a direct stake in pending legislation."

Sen. Carl Levin (D-MI) (Photo: CNN)

That $20 million figure is certainly impressive. But the story never defines its terminology: Should the private-equity giant Carlyle Group be classified as an "energy interest," given that it has stakes in 40 energy companies, or as an unrelated financial firm?

And given that Republicans, with the exception of Sen. Lindsey Graham (R-SC), have shown little willingness to negotiate on pending climate legislation, why attach the "fence-sitter" label to senators such as John McCain (R-AZ) — who days ago slammed the chamber’s bill as "horrendous"?

But Greenwire’s calculations are worth re-running because they smartly combine the transportation and electricity industries into one bloc. As electrified transport continues to command Washington’s attention, automakers and power providers are finding their priorities increasingly in alignment — and their lobbying goals coalescing around similar government support.

Of the 27 senators deemed climate fence-sitters by Greenwire, 17 are
Democrats. Using data from the non-partisan Center for Responsive
Politics (which only dates back 20 years), Streetsblog Capitol Hill ran
down the numbers on how much campaign money those 17 senators received
from the transportation and electricity interests that ranked among
their top 20 donors.

The final tally: $2.3 million, broken down by senator in the chart at right. The Senate Democrats who hauled in the most from the transport and electricity sectors were Michigan’s Carl Levin and Debbie Stabenow, who maintain close ties to the domestic automakers in their home state, and Byron Dorgan (ND), whose top career donors included Northwest Airlines and the United Transportation Union.

As President Obama prepares to visit global climate talks in Copenhagen next month bearing a U.S. emissions reduction target that tracks the already-passed House legislation, all eyes will turn to the Senate’s precarious political dynamics.

In the upper chamber, Finance Committee Chairman Max Baucus (MT) — among the 17 undecided Democrats on the climate bill — is eyeing a January markup of the revenue allocations approved earlier this month by Barbara Boxer’s (D-CA) environment committee.

Boxer’s version of the legislation included hundreds of millions of dollars in annual grants for transit, land use planning, and other clean transport projects, but it’s unclear whether Baucus is prepared to keep that funding alive.

On the electricity front, the Senate bill also includes a national renewables standard that aims to make transit systems — as well as much-touted plug-in hybrid autos — run on greener power. But some fence-sitting Democrats, such as Sen. Jim Webb (VA), are pushing for greater consideration of nuclear power as a renewable energy source.

With a lengthy climate debate poised to cement the Senate’s self-created reputation as "the world’s greatest deliberative body," the transportation decisions made by the 17 undecided Democrats are worth watching closely.