Three things to know about Trump's "pocket rescission:"
1. Withholding funds until they expire is illegal
2. SCOTUS has not yet ruled on this issue
3. So many unobligated funds this late in the fiscal year is a problem in and of itself
citizensforethics.org
Three things you need to know about Trump’s “pocket rescission” proposal - CREW | Citizens for Responsibility and Ethics in Washington
Trump's proposed so-called “pocket rescission,” which attempts to claw back $810 million in funds appropriated by Congress, is illegal.