At a glance, Republicans must have been thrilled to learn that Trump is now backing a massive, deficit-increasing corporate tax rate cut. But in his haste to rush a blueprint out the door ahead of his 100th day in office this Saturday, Trump committed his administration to a plan that very likely won’t work, even if Republicans in Congress support it unanimously.

The Bush tax cuts ultimately expired because they were enacted through the congressional budget process. Bills passed through this process can’t be filibustered, but also can’t be used to enact legislation that increases deficits outside of the budget window. To get around this problem, Republicans in 2001 included a 10-year sunset provision in the tax cuts, and passed them with less than 60 votes.

Ahead of Trump’s inauguration, congressional Republicans led by House Speaker Paul Ryan drew up a moonshot plan to make their tax cuts permanent, one that dovetailed with their rallying cry for the better part of a decade. A swift repeal of the Affordable Care Act, including the law’s revenue streams, would have been a large, permanent tax cut unto itself. Once Obamacare’s taxes were gone, the thinking went, Republicans could tinker further with the code without worrying about increasing deficits, because they would have already secured their revenue cut.

Trump took just enough ownership of the GOP repeal plan–known as the American Health Care Act–that the doomed effort became known as “Trumpcare.” But the president never bothered to learn the details of the legislation, or persuade the public and members of Congress of its merits.

He also, apparently, never bothered to learn the ins and outs of the budget reconciliation process, or how it might interact with certain changes to the tax codes.