Hoeven, Democratic Sen. Max Baucus of Montana, and 16 others signed a letter to Obama calling on him to approve the deal now that Nebraska's concerns have been resolved.
But Obama faces significant pressure from an engaged environmental lobby to block the plan, particularly in light of his groundbreaking comments on climate change in his second inaugural address.
"You cannot say the words the president did in his inaugural address, and then turn around and approve the pipeline," said Jane Kleeb with BOLD Nebraska, an advocacy group opposed to the plan. "This much is as crystal clear as the Ogallala Aquifer is without this risky export tar sands pipeline."
Environmental advocates say the refining of tar sands to oil is particularly dangerous and dirty, producing plumes of gases that contribute to global warming. They also note the destruction of natural landscape in the construction process and potential for habitat-destroying spills.
Activists plan a major rally against the pipeline on the National Mall later next month.
"Together we'll send the message loud and clear," said leading environmental activist and author Bill McKibben on his blog, "'If you're serious about protecting future generations from climate change, stop the Keystone XL tar sands pipeline. If you can do that, Mr. President, we can all work together to help build a climate legacy that will be a credit to your critical eight years in office.'"
With the election in the rearview mirror and no pressure of a campaign for a second term, Obama may feel freer to buck the protests from environmental and progressive groups, particularly since other key constituencies in his base -- including labor unions -- are for the pipeline plan.
"My general attitude is what is best for the American people? What's best for our economy both short term and long term? But also, what's best for the health of the American people?" Obama explained of his thinking during a November 2011 interview on the pipeline plan, before he later tabled the decision for further review.
"I recognize all the political pressure the president faces," Boehner said Tuesday, "but with our energy security at stake and many jobs in limbo, he should find a way to say yes."