Everyone knows how unconscionably rushed and sloppy the Republican tax bill was. What's gotten less focus is how the ineptitude of the process may pay future budget-rules benefits to the Republicans.
Suppose we start from the bill's estimated $1.4 trillion ten-year cost (ignoring for now the "dynamic" issues that the Joint Committee thought might lower it to $1 trillion - although better estimates by analysts with greater independence from political pressure show less offset than this).
Now suppose that two drafting errors or omissions, triggering massive tax avoidance responses that the JCT did not anticipate, turn out to have 10-year budgetary costs of $100 billion each.
Suppose that Blunder #1 goes to people the Republican leadership likes, such as business owners who take unexpected unadvantage of the lower corporate rate, fun and games with passthroughs, etc.
All they have to do is leave this in place, and they get to shower $100 billion more on their friends, who will be duly grateful, without its ever appearing in a revenue score.
Now suppose that Blunder # 2 goes to people the Republican leadership doesn't like, such as blue state professionals who end up, one way or another, getting the equivalent of extra state and local income tax deductions due to countermeasures that they and their state legislatures develop.
Say this triggers "technical corrections" to take away the extra $100 billion that people have figured out how to save in taxes, via gaps and mistakes in the original drafting. In effect, this retroactively causes the original revenue estimate for repealing the deduction to be correct after all. Only, the Congressional Republicans get budgetary credit for a $100 billion revenue increase that would have been denied them, had they drafted the bill more competently upfront. And there's no sort of budget-rules offset for the fact that the 2017 revenue estimate, based on what was actually enacted, ought to have been $100 billion higher, purely as a matter of logical consistency. So upfront incompetence is potentially all upside for these guys.