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Amid a social media feud between President Trump and California Gov. Gavin Newsom, the federal government announced its intention Tuesday to cancel nearly $1 billion in pending funding for the state's long-planned, high-speed train.

In a letter to California High-Speed Rail Authority CEO Brian P. Kelly on Tuesday, the U.S. Department of Transportation outlined the government's reasons for pulling funding. The state has not come up with its own promised funding, will miss a 2022 completion target and has recently reconfigured the project outside the bounds of a federal pact for funding, railroad chief Ronald L. Batory wrote.

The federal department will "de-obligate" $928,620,000 in promised cash, but California will be given a chance to argue its case, Batory said in the letter. He also said the Trump administration is "exploring all available legal options" to recover $2.5 billion in past federal grants for the project.

An illustration of California's high-speed rail project. CA.gov

Newsom last week announced plans to scale back the $77 billion project. Rather than taking travelers between Los Angeles and San Francisco as originally envisioned, the train will now seek to bridge the Central Valley cities of Bakersfield and Merced.

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Construction of that 160-mile stretch is underway.

Trump reacted to Newsom's announcement on Twitter last week: "California has been forced to cancel the massive bullet train project after having spent and wasted many billions of dollars. They owe the Federal Government three and a half billion dollars. We want that money back now. Whole project is a 'green' disaster!"

The governor responded by noting that the project had not been scrapped and that the president was "desperately searching" for money to fund his proposed border wall.

That’s an apparent reference to Governor Newsom’s announcement last week that he plans to scale back the project, amid ballooning costs.

On Tuesday, Newsom argued that the funding U-turn was more about California's opposition to Trump's declaration of emergency at the U.S.-Mexico border than the efficacy or evolution of the train project, which has long been opposed by the state and national Republican establishment.

California on Monday joined 15 other states in a lawsuit challenging Trump's emergency declaration, which allows the president to tap into funds unapproved by Congress for a border wall.

"It’s no coincidence that the Administration’s threat comes 24 hours after California led 16 states in challenging the President’s farcical 'national emergency,'" Newsom said in a statement. "The President even tied the two issues together in a tweet this morning. This is clear political retribution by President Trump, and we won’t sit idly by. This is California’s money, and we are going to fight for it."

As I predicted, 16 states, led mostly by Open Border Democrats and the Radical Left, have filed a lawsuit in, of course, the 9th Circuit! California, the state that has wasted billions of dollars on their out of control Fast Train, with no hope of completion, seems in charge! — Donald J. Trump (@realDonaldTrump) February 19, 2019

The White House pushed back against the accusations of political retribution against California for leading the legal fight against Trump's emergency declaration.

"The California governor himself acknowledged last week that this project costs too much and will never be constructed as planned," the White House said. "In light of this recognition, the Trump administration has a responsibility to all taxpayers to cancel the financial support for this boondoggle.”

State Sen. Scott Wiener, D-San Francisco, said the state is not ready to concede. "We will fight this illegal action as we have with many of this administration’s unlawful undertaking," he said in a statement. "This is about California’s future, and we will not back down."

But state Assemblyman Vince Fong, a Central Valley Republican, called for the end of the high-speed project. "Continuing to throw hard-earned tax dollars at a structurally flawed project is fiscally irresponsible, and I believe we need to scrap this project entirely," he said in a statement to NBC News.