So far, $15.7 billion has been invested in the project, with $2.7 billion spent by the federal government. Duffy said he is directing the Federal Railroad Administration to investigate whether the Trump administration should keep the Biden administration’s promise to give an additional $4 billion.

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.