Members walk down the steps of the House side of the US Capitol after voting on the Kyestone XL Pipeline, Nov. 14, 2014.
Mark Wilson—Getty Images
By Lily Rothman
November 18, 2014

On Friday, as the House voted to approve a proposal for the long-debated Keystone Pipeline, we rounded up TIME’s past coverage of the environmental questions behind the controversial pipeline — but, with the Senate is expected to vote Tuesday on their own version of the proposal, it’s clear that the environmental impact isn’t the only factor influencing decision-making.

As these three stories make clear, the politics are nearly as complex as the science:

July 22, 2013: Beyond the Keystone Pipeline

Michael Grunwald posits that the energy agenda could be a big part of President Obama’s legacy, and that there are reasons beyond the climate why he might want to veto the pipeline even if the legislature approves it, as has been suggested he will:

Nov. 13, 2014: The Politics Behind Mary Landrieu’s Pipeline Power Play

Alex Rogers analyzes Senator Mary Landrieu’s call for the Senate to bring the matter to a vote:

Nov. 13, 2014: GOP Prepares for an Energy Battle

Denver Nicks takes a look at broader feelings about energy and the environment among the Republican leadership, revealing that the pipeline is just the beginning:

Write to Lily Rothman at lily.rothman@time.com.

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