US President Donald Trump’s Golden Dome missile defence shield will cost as much as US$1.2 trillion to deploy and operate, six times above current forecasts, according to a new estimate – and would still probably fail to stop an all-out attack.

The new forecast from the non-partisan Congressional Budget Office relies on capabilities spelled out in Trump’s January 2025 executive order unveiling the idea rather than any government plan because the administration has given no details about what the system will look like, it said.

That makes it “impossible to estimate the long-term cost of the system being contemplated”, CBO said. Golden Dome would be operational for 20 years, the CBO said, but “the system could be overwhelmed by a full-scale attack mounted by a peer or near-peer adversary”.

The report was requested almost a year ago by Oregon Senator Jeff Merkley, the top Democrat on the Senate Budget Committee. In a statement, he called Golden Dome a “massive giveaway to defence contractors paid for by working Americans”.

“I will continue to work with my colleagues to prevent another dime from flowing to this racket,” Merkley said.

The cost cited in the CBO’s 12-page assessment compares to an estimate of US$185 billion that the director of the Golden Dome programme, US Space Force General Michael Guetlein, disclosed in March.