Trump is a idiot. He kills a public works project that is needed and has been agreed to by two states. He wants to redo the project which will take years to redo and will cost even more due because big public works projects take a lot of time because of the number of stakeholders involved. What is efficient in redoing a done deal? It will cost even more now due to the fact that the process will have to be start from square one. There was no downside for the federal government because the money on the fed side was in the form of loans that were repaid by NJ and NY. Huge public works projects take time. FYI the Denver International Airport project took about 13 years to complete. The Gateway project is of comparable complexity.
But wait it is a political ploy to get Sen. Schumer (D-NY) on the Trump infrastructure bill. By cancelling this done deal Trump is trying to fold any new Gateway project into his infrastructure bill, that has not been written yet, as a heavy handed way to create "bipartisan" votes in the Senate in 2018.
Trump administration kills Gateway tunnel deal | Crain's New York Business