The G.A.O. decision goes to the heart of both the impeachment inquiry and our constitutional system of separated powers — and puts congressional Republicans in the hot seat. A violation of the Impoundment Control Act in connection with the Ukraine funds is directly relevant to the first article of impeachment because it is a mechanism by which the president executed the alleged abuse of power. The question of access to information about that violation is directly relevant to the second article of impeachment — obstruction of Congress. What is at stake is the status of Congress as a coequal branch of government. Much as Senate Republicans seem eager to, they — indeed, the entire Senate — cannot turn away from testimony and documents relevant to the articles of impeachment, however inconvenient the timing.

The G.A.O. decision addresses a rather narrow appropriations law issue. In short, what the president did here was precisely the type of adventurism the Impoundment Control Act was designed to prevent. The O.M.B. had no authority to withhold the funds because the act permits it only under specific circumstances — and in this instance, those weren’t met. The O.M.B. argued that the funds were withheld because doing so was necessary to ensure that they were not spent “in a manner that could conflict with the president’s foreign policy.” But the G.A.O. decided the withholding was an “impermissible policy deferral.”

The decision also renders a judgment that the withholding was not a mere delay, as the O.M.B. argued. Program execution was “well underway” when the O.M.B. held back the funds, and “there was no external factor causing an unavoidable delay.”

More broadly, the G.A.O. decision represents an assertion of Congress’s constitutional power of the purse. The G.A.O. is well respected, and historically the executive branch has given substantial deference to its opinions. In any other administration, this decision would have been an earthquake reverberating across the executive branch.

In this administration, the import of the decision is unclear. A Nov. 5, 2019, memorandum instructed federal agencies that they are under no obligation to comply with the legal decisions issued by the G.A.O. because those decisions are part of the legislative branch and are therefore not binding on the executive branch. As a technical matter, that is true, but the president must faithfully execute the laws, including the Impoundment Control Act. Instead, executive branch machinations in the Times report indicate that O.M.B. lawyers were working up an argument that Mr. Trump’s role as commander in chief would allow him to override Congress. Such thinking is consistent with Mr. Trump’s unprecedented stonewall approach to Congress more generally — like his assertion that he has “an Article Two where I have the right to do whatever I want as president,” his lawyers’ direction of total noncooperation with Congress’s investigation into the Ukraine matter and his refusal to participate at all in the House impeachment proceedings.