It's shaping up to be one of the trickiest decisions President Obama will have to make early in his second term: whether to approve construction of the 1,700-mile Keystone XL oil pipeline, stretching from Alberta, Canada, to Oklahoma.

Nebraska Gov. Dave Heineman, a Republican, on Tuesday endorsed a revised pipeline route through his state, removing a final hurdle for the $5 billion project on the state level. Governors and congressional delegations from the four other states it crosses have already pressed for federal government approval.

The fate of the project now rests squarely with the Obama administration, which has the final say because it crosses an international boundary.

For the White House, the issue is a perfect storm of competing interests: the promise of thousands of new construction jobs and potential for cheaper energy, but with stiff opposition from environmental groups that say the pipeline would mean a toxic injection of greenhouse gases into the atmosphere and heightened risk of destructive spills.