Timeline: Notable events surrounding the Keystone XL oil pipeline

The U.S. State Department issues a presidential permit for a $5.2 billion Keystone pipeline to transport crude oil.

TransCanada files paperwork to expand the existing Keystone pipeline with a new Keystone XL route. The pipeline would extend from Canada's tar sands through Montana, South Dakota and Nebraska, where it would connect with the existing Keystone pipeline route to carry more than 800,000 barrels of crude oil a day to specialized refineries along the Texas Gulf Coast.

First Keystone pipeline goes into operation.

As the permit is reviewed, then-Secretary of State Hillary Rodham Clinton says the department is "inclined" to approve project. The project begins to galvanize the environmental movement to pressure the Obama administration to act on climate change. Republicans and other project supporters argue the project will create jobs and help the economy.

Then-Nebraska Gov. Dave Heineman sends a letter to President Barack Obama asking that the proposed Keystone XL pipeline avoid the Sandhills, an area consisting of fragile, grass-covered sand dunes in western Nebraska.

The U.S. State Department issues its final environmental impact statement determining "there would be no significant impacts to most resources along the proposed project corridor."

Amid growing public resistance to the Keystone XL, Heineman calls lawmakers into a special session to address environmental concerns in Nebraska. Lawmakers approve a pipeline siting law that requires companies to apply through an independent state commission. Obama announces a delay, pushing off the decision until after his re-election campaign. His administration says other potential routes through Nebraska need to be studied.

Congress tries to force Obama's hand by passing legislation requiring approval of the Keystone XL pipeline within 60 days unless the president determines the project does not serve the national interest. Weeks later, Obama rejected the application but allowed TransCanada to re-apply.

Nebraska lawmakers rewrite the pipeline law to give the governor the power to approve the Keystone XL route through the state.

TransCanada reapplies and restarts the federal review process.

The State Department issues an environmental review that raises no major objections to the Keystone XL oil pipeline and says other options to get oil from Canada to Gulf Coast refineries are worse for climate change.

Obama declares he will only approve the project if it doesn't worsen carbon pollution. "Our national interest would be served only if this project does not significantly exacerbate the problem of carbon pollution," Obama says in a speech declaring that fighting climate change will be a major priority his second term.

The State Department releases another final environmental impact statement, again voicing no major environmental objections to the project.

A Nebraska judge overturns the state law that allowed the pipeline, throwing the project into legal limbo.

The State Department announces it is again delaying its review, citing the legal dispute over the Nebraska route.

TransCanada files legal papers in nine Nebraska counties to invoke eminent domain for the land that's needed to construct, operate and maintain the pipeline.

Congress again tries to push the Obama administration to decide on the permit by passing legislation forcing the decision and sending it to the White House. Obama vetoes the bill days later.

Clinton, now seeking the Democratic nomination for president, says she opposes construction of the Keystone pipeline.

As it appears increasingly likely that Obama will reject the pipeline, TransCanada asks the administration to suspend the company's application. The State Department reviews the request for a day, and then rejects it.

Obama announces he is rejecting the permit to build the Keystone pipeline. The project is not in the national interest, he says. "America is now a global leader when it comes to taking serious action to fight climate change. And frankly, approving this project would have undercut that global leadership," he says.

TransCanada seeks $15 billion in damages from the federal government in response to the Obama administration rejecting the Keystone XL pipeline.

 President Donald Trump signs executive actions to advance the construction of the Keystone XL pipeline, along with the four-state Dakota Access oil pipeline.