Clinical trials that require specific supplies (e.g. blood test reagents or a special drug delivery system) have to stop if the research lab/clinical entity can’t buy those supplies. If this happens in the middle of a long study, it could make all of the data collected thus far worthless. You could lose an entire study, and create a situation where participants took on risk but the benefit (research results) never materializes. Stopping all NIH purchasing is a problem.