Trump can't be trusted to keep his word.

And he can use Recission to cut spending after appropriations. As explained below, he can cut spending for 45 days after which, by a simple majority vote in both houses, Congress can approve his actions without use of the filibuster.

“The rescissions process laid out in the Budget and Impoundment Control Act of 1974 provides lawmakers the opportunity to reduce spending on an expedited basis. Following formal submission of a rescissions package, the president can withhold funds for 45 days (excluding any days in recess), during which time Congress can consider the legislation.

Because the legislation is considered privileged in the Senate, passage is not subject to a filibuster. As a result, enacting the Trump administration rescissions package could occur with 218 Republican votes in the House and 51 Republican votes in the Senate — at least in theory.”