President Barack Obama is running out of reasons to say no to Keystone XL, the proposed oil pipeline that's long been looming over his environmental legacy.

Five years after the pipeline's backers first asked the Obama administration for approval, the project remains in limbo. It's stuck in a complex permitting process that has enabled Obama to put off what will inevitably be a politically explosive decision.

But a long-awaited government report released Friday removes one excuse for delay. The State Department's report raised no major environmental objections to the pipeline.

Keystone has become a proxy for the broader battle over energy-versus-environment. So Obama's decision will have an outsized impact on his environmental legacy. Obama has launched a push to try to curb global warming.