The Trump administration has launched an investigation into California’s high-speed rail project in what could be the first step in clawing back the $4 billion promised by the Biden administration to build out the first section of the line, from Merced to Bakersfield.

President Donald Trump canceled nearly $1 billion in federal funding for the high-speed rail project in 2019, during his first term. The Biden administration later restored the funding and, in December 2023, allocated $3.3 billion more.

The Trump administration said Thursday it is opening a review into whether to rescind about $4 billion awarded to California's High-Speed Rail project.

The transportation secretary, Sean Duffy, said the government would conduct a “compliance review” on a $3.1 billion grant, potentially threatening the viability of the troubled project.

While U.S. Transportation Secretary Sean Duffy questioned the cross-state high-speed rail project, he praised the Las Vegas-to-Los Angeles effort.

Republicans have long targeted high-speed rail, despite its popularity with a majority of Californians. U.S. Rep. Kevin Kiley, who appeared with Duffy and introduced legislation in December to defund it, blasted the railway as “the worst public infrastructure failure in U.S. history.”

Duffy, speaking at Union Station in Los Angeles on Thursday morning, said the Federal Railroad Administration will review the rail project and its leadership.

Secretary of Transportation Sean Duffy said the California high-speed rail project will continue to cost taxpayers billions of dollars with no definitive timeline for completion.