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DENVER — Colorado Sen. Michael Bennet was greeted by protestors on Capitol Hill Tuesday hours ahead of a vote on the Keystone XL pipeline that ultimately failed by one vote.

Senate Democrats defeated the proposal on a 59-41 vote, leaving the bill’s sponsor, Sen. Mary Landrieu, D-Louisiana, and Republican backers one vote short of the 60-vote filibuster-proof threshold.

Environmental activists targeted Bennet and other Democrats who have signaled their support for the legislation to approve construction of the pipeline to transport oil from Alberta, Canada to the Gulf of Mexico.

Josh Fox, the director of the anti-drilling documentary Gasland, appears to have been part of the protest, posting a picture of the activists inside Bennet’s office on Twitter.

The scene inside Bennet’s Capitol Hill offices Tuesday follows a similar gathering of protestors at the lawmaker’s Denver office on Monday.

“We continue to hear intense advocacy from Coloradans on this issue,” said Adam Bozzi, Bennet’s spokesman.

The Senate vote was largely about pure politics: the legislation is sponsored by Sen. Mary Landrieu, D-Louisiana, who faces a runoff in a few weeks and was looking to demonstrate her support for the state’s oil and gas industry; her opponent, GOP Congressman Bill Cassidy, is the sponsor of a House version of the same bill that was approved last week.

Bennet, who is up for reelection in 2016, reaffirmed his support for building the pipeline last week, giving Landrieu 59 known yes votes on the measure, one short of a filibuster-proof majority.

“Senator Bennet voted in support of the Landrieu bill,” Bozzi said. “He would prefer that instead of focusing our political debate on a narrow issue that we develop a broad and comprehensive energy strategy to reduce carbon pollution and support renewable energy. He believes we should take aggressive action to curb climate change and support the President’s Climate Action Plan.”

Bennet’s decision to vote with 13 other Democrats and all senate Republicans only strengthens his centrist credentials, which serve him well in a purple state like Colorado, although conservationist Democrats weren’t pleased about it.

“We applaud Senator Udall for opposing the pipeline and are disappointed that Senator Bennet supported this ill conceived project,” said Conservation Colorado’s Pete Maysmith.

Landrieu’s failure to find a 60th vote, seemingly a sign that her fellow Democrats either didn’t think the vote would save her or that she was worth spending their own political capital to save, is a political setback, but not a fatal blow to the legislation itself, which will have more than the 60 votes needed to pass the senate once Republicans take over in January.

Even if Landrieu had secured a 60th vote and the senate had approved the measure Tuesday afternoon, President Obama was likely to veto it.

Colorado Sen. Mark Udall, a Democrat who lost his reelection bid earlier this month, voted against the legislation.

His successor, GOP Senator-elect Cory Gardner, has been a strong supporter of the Keystone pipeline.