Republicans on Capitol Hill are reportedly planning to use the filibuster-proof budget reconciliation process to repeal the Affordable Care Act and overhaul the tax code. Against that background, Sam Wice says that “the most powerful person in America” in 2017 will be Senate Parliamentarian Elizabeth MacDonough, the nonpartisan official who will “determine” how much of their agenda Republicans can pass through reconciliation. This, of course, is an exaggeration: like it or not, the most powerful person in America in 2017 will be Donald J. Trump, who will wield all the power of the imperial presidency. But Wice’s post helpfully directs our attention to the budget reconciliation process, the rules of which quite likely will determine whether the Republican leadership on Capitol Hill can repeal the ACA and reform the tax laws.

Yet while one should not underestimate the importance of reconciliation, one should also not overestimate the power of the Parliamentarian in the reconciliation process. As a formal matter, the Parliamentarian’s role is advisory; and as a practical matter, the Parliamentarian has little say over significant aspects of reconciliation. Other actors—most notably, Senate Budget Committee Chairman Mike Enzi (R-Wy.)—wield at least as much influence as the Parliamentarian.  Most importantly, Enzi—not MacDonough—will determine whether the provisions in any reconciliation bill violate various rules against deficit-increasing legislation being passed via reconciliation. And unlike the Parliamentarian, the Budget Committee Chairman is very hard to fire.

Reconciliation measures can begin in either or both chambers. However, since the ultimate vote on the budget measure occurs in the Senate, we’ll focus on the Senate side of the reconciliation process for purposes of this discussion. On the House side, the Rules Committee Chair and the Budget Committee Chair will wield outsized influence as well. We expect Pete Sessions (R-Tex.) to stay on as House Rules Committee Chair; as for the House Budget Committee Chair, the race is on for a replacement to Tom Price, the Georgia Republican recently tapped as Trump’s Health and Human Services Secretary.

To understand why the Budget Committee Chair is as powerful as he is, a bit of background on reconciliation may be helpful. As Wice notes, “[b]udget reconciliation is a method of passing legislation in the Senate that avoids a filibuster.” (The reconciliation rules apply to the House as well, but in the House, there is no filibuster to avoid.)  The basic rules are set out in Title III of the Congressional Budget and Impoundment Control Act of 1974, codified as amended at 6 U.S.C. §§ 631—645a. The amendments matter, and one such amendment matters more than the others: the so-called Byrd rule, named after the longtime Democratic senator from West Virginia and codified at 2 U.S.C. § 644, imposes substantive limits on the sorts of provisions that can be enacted via reconciliation. (For reasons that don’t matter, 2 U.S.C. § 644 is more commonly referred to as section 313 of the Congressional Budget Act; we’ll use the more common reference here, but know that if you’re looking for section 313 in the U.S. Code, 2 U.S.C. § 644 is where to go.)

The text of the Byrd rule is worth reading in full—you’ll likely be hearing a lot about it over the next several months—but one subparagraph, section 313(b)(1)(E), deserve special attention:

[A] provision shall be considered to be extraneous if it increases, or would increase, net outlays, or if it decreases, or would decrease, revenues during a fiscal year after the fiscal years covered by such reconciliation bill or reconciliation resolution, and such increases or decreases are greater than outlay reductions or revenue increases resulting from other provisions in such title in such year . . . .

This critical provision is intended to be the backstop to balancing the budget. If one wants a tax cut or an increase in spending that widens the deficit outside the years covered by the reconciliation resolution, something else must go. Or, at least, that was an intention animating the Byrd rule (though as discussed below, the effect is sometimes quite the opposite).

But to enforce the Byrd rule, who decides whether a provision in a reconciliation bill is “extraneous”? Wice assumes it will be the Parliamentarian. Technically, it’s the “Presiding Officer” of the Senate (see section 313(e)). Under Article I, Section 3, clause 4 of the Constitution, the Vice President is the Presiding Officer of the Senate when he’s there; more commonly, the Presiding Officer is the Senate’s President pro tempore (currently Orrin Hatch) or a more junior senator from the majority party designated by the President pro tempore as his stand-in.

In practice, the Presiding Officer generally consults the Parliamentarian and “almost never” fails to follow the Parliamentarian’s recommendation. But the Presiding Officer retains the option to do as he pleases (or as Senate Majority Leader Mitch McConnell instructs). As one of McConnell’s predecessors, Trent Lott, previously  put it: “The presiding officer rules. The parliamentarian is a human being.” (One might have thought that Orrin Hatch was also a human being, in addition to being a performing artist, hip-hop Hanukkah songwriter, and occasional “Parks and Rec” star . . . but that’s all, shall we say, “extraneous.”)

And not only can the majority party disregard the Senate Parliamentarian’s rulings, but it can fire the Parliamentarian too. Majority Leader Lott did just that in 2001 after the Senate Parliamentarian ruled that a disaster relief provision in a reconciliation bill was extraneous.

Yet even if the Republican leadership keeps MacDonough around and follows her recommendations, MacDonough’s power remains constrained. That’s because, as a matter of Senate practice (and House rule), the Budget Committee Chair—and not the Presiding Officer or the Parliamentarian—provides “authoritative guidance” regarding the budgetary impact of reconciliation measures.

How might the Budget Committee Chair exercise this guidance power? The debate over the Tax Increase Prevention and Reconciliation Act of 2005 (TIPRA) provides a stark example. TIPRA was enacted pursuant to a reconciliation resolution covering fiscal years 2005 to 2010. That meant, per section 313(b)(1)(E), that a provision would be extraneous if it would decrease revenues in a fiscal year after 2010. One of the provisions in TIPRA extended the 15% preferential rate for long-term capital gains and qualified dividends through 2010 (under then-current law, the 15% rate was set to rise to 35% after 2008). The extension of the 15% rate would decrease revenues outside the reconciliation resolution window because individuals would realize gains at a lower rate in 2010 rather than paying the higher rate in later years.

So how did the Senate Republicans nonetheless enact TIPRA via reconciliation? Easy. They made sure that such decreases would be offset by revenue increases resulting from other provisions in TIPRA. Most significantly, they allowed high-income taxpayers to convert their traditional IRAs into Roth IRAs beginning in 2010. When an individual converts a traditional IRA into a Roth, she pays tax today with the expectation that she’ll save on taxes in the future—either because she’ll be in a higher bracket when she takes distributions, or because she wants her money to continue to grow in the IRA tax-free and the Roth rules allow her to forgo any distributions until death.

Wait, you ask, how could the revenue raised in the short term from traditional-to-Roth IRA conversions offset the revenue decrease outside the reconciliation window resulting from the extension of the 15% capital gains and dividend rate? After all, if individuals are converting from traditional IRAs to Roths because they think that conversion will reduce their lifetime tax bills, then wouldn’t the Roth IRA provision in TIPRA reduce long-run government revenues? At first blush, one might think that the Roth IRA provision makes the Byrd rule violation even worse: the extension of the 15% capital gains and dividend rate reduces revenues outside the window, and conversions from traditional to Roth IRAs reduce long-run revenues even more. It would seem that either taxpayers who roll over into Roth IRAs are being dumb and converting against their own interest, or the Parliamentarian is dumb to fall for this gimmick.

And there’s the catch (or, rather, the failure of the Byrd rule). The Parliamentarian had no say in the matter. Senate Budget Committee Chair Judd Gregg decided that the Roth provision, along with certain others, offset the out-year revenue effects of the capital gains and dividends rate extension—and the Senate Budget Committee Chair has the last word when it comes to the budgetary impact of reconciliation measures. Gregg’s rationale, apparently, was that the Roth IRA provision would raise revenue from 2011 to 2015, and any effects beyond 2015 were too far in the future to estimate accurately. For more on the episode, see George K. Yin, Temporary-Effect Legislation, Political Accountability, and Fiscal Restraint, 84 N.Y.U. L. Rev. 174, 222-224 (2009).

Next year may be 2006 all over again. President Trump wants to eliminate the Affordable Care Act’s 3.8% net investment income tax, wants to repeal the estate and gift taxes, and wants to allow U.S. corporations to bring home foreign profits while paying a holiday repatriation tax at a reduced 10% rate. All of those provisions—even if enacted as temporary measures in a reconciliation bill—would have long-run revenue effects: investors would realize gains before the 3.8% tax returns; high net worth individuals would make large gifts to their children now before the estate and gift taxes come back, and corporations would repatriate earnings during the holiday instead of potentially paying a higher tax later on. And so to offset the out-year effects of those temporary provisions, the Republicans are going to need some revenue-raisers. Will gimmicks like the Roth IRA trick work this time? Will Congress rely on dynamic scoring to estimate the out-year budgetary impacts of the Trump tax plan? In the Senate, these aren’t questions for Elizabeth MacDonough. They’re questions for Mike Enzi.

There is much more to be said about reconciliation than this—the two of us are working on an article tentatively titled “The Law of Reconciliation” that explores the nuances of the congressional budget process in greater detail. Watch this space for more on the subject. And in the meantime, keep your eyes on the senior Senator from Wyoming. He won’t be the most powerful man in town (that man will live at 1600 Pennsylvania Avenue, and sometimes at 721 Fifth Avenue, and sometimes at 1100 South Ocean Boulevard). But when it comes to budget reconciliation, Mike Enzi may be the man holding the trump card.

Daniel Hemel is an assistant professor of law at the University of Chicago. David Herzig is a professor of law at Valparaiso University.