European leaders, eyeing crucial gaps in their countries’ defense capabilities, are still holding out hope that Donald Trump will make good on his offer to give Ukraine concrete security guarantees, even as a negotiated peace looks increasingly improbable.

Europe has critical shortfalls in space-based intelligence and surveillance, and integrated air and missile defense — the primary areas that the U.K.— and French-led coalition of the willing hopes U.S. assistance will cover. It would cost Europe $1 trillion to replace conventional U.S. military capabilities assigned to the region, according to an International Institute for Strategic Studies report published last week.

The U.S. provides most of NATO’s intelligence, surveillance and reconnaissance, including satellites, which has proved critical in the response to Vladimir Putin’s invasion of Ukraine. Replacing that would cost Europe $4.8 billion, according to the report, "Progress and Shortfalls in Europe’s Defense.” European officials say the U.S. must continue to provide that under a peace deal, so Ukrainian and European forces can be alerted to any Russian breach.