The second law of thermodynamics tell us that some macroscopic processes tend to run only one direction. It's easier to disperse a drop of ink in a glass of water than to somehow reconstitute the drop of ink once the glass has been stirred.
In general, the response of a system to some input (say the response of a ferromagnet to an applied magnetic field, or the deformation of a blob of silly putty in response to an applied stress) can depend on the history of the material. Taking the input from A to B and back to A doesn't necessarily return the system to its original state. Cycling the input and ending up with a looping trajectory of the system in response because of that history dependence is called hysteresis. This happens because there is some inherent time scale for the system to respond to inputs, and if it can't keep up, there is lag.
The proposed budget would make sweeping changes to programs and efforts that, in some cases, took decades to put in place. Drastically reducing the size and scope of federal agencies is not something that can simply be undone by the next Congress or the next President. Cutting 20% of NIH or 17% of DOE Office of Science would have ripple effects for many years, and anyone who has worked in a large institution knows that big cuts are almost never restored. Expertise at EPA and NOAA can't just be rebuilt once eliminated.
People can have legitimate discussions and differences of opinion about the role of the government and what it should be funding. However, everyone should recognize that these are serious decisions, many of which are irreversible in practical terms. Acting otherwise is irresponsible and foolish.