House and Senate Republicans have been working for months on a sweeping piece of legislation addressing a litany of President Donald Trump's agenda items.
Such a bill is possible via the budget reconciliation process, which allows the party controlling Congress and the White House to pass broad policy overhauls while totally sidelining the minority. It lowers the Senate's threshold for passage from 60 votes to 51, lining it up with the House's simple majority rules.
However, one of the caveats is that the measures tucked into the bill must deal with taxes, spending or the national debt. One key person gets the final say over what is relevant to that sphere - the Senate parliamentarian.
The parliamentarian, who heads the Senate's parliamentarian office, is a nonpartisan, unelected role appointed by the Senate majority leader. It does not have a fixed term.
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The person's role is to advise the Senate and its staff on the chamber's rules and precedent. The normally low-profile role has been thrust into the spotlight several times in congressional history, however, particularly surrounding reconciliation.
"At the end of the day, it really is a judgment call. And sometimes you're making a judgment call where you're relying on similar situations or maybe analogous situations where we dealt with reconciliation in the past, maybe other times you're dealing with a completely novel issue, and you're having to figure it out," one former senior Senate aide described to Fox News Digital.
"Or maybe, and this happens a lot, people are trying get things through, debating or citing past provisions of previous reconciliation bills…saying 'Hey, this provision is very similar, and this got through.'"
The Senate parliamentarian leads the "Byrd bath," a key part of the reconciliation process where the legislation is carefully examined, and any measures found not relevant to the contours of reconciliation are stripped out.
Notably, progressive Rep. Ilhan Omar, D-Minn., called for the firing of the Senate parliamentarian in 2021 when she forced Senate Democrats to scuttle their $15 per hour minimum wage effort from their reconciliation bill at the time.
That same parliamentarian, Elizabeth MacDonough, who was appointed by the late former Senate Majority Leader Harry Reid, D-Nev., is still serving today and has largely garnered bipartisan respect for her handling of the role.
MacDonough, appointed in 2012, is the first woman in the job. She was a part of the parliamentarian's office before that and briefly served as an attorney in the Department of Justice, according to NPR.
"I would say that this particular parliamentarian sees herself more as, almost an administrative law judge, and I think that she has generally viewed some of the things that the Senate has been allowed to get away with in reconciliation as a departure from precedent," said Paul Winfree, president of the Economic Policy Innovation Center and a former Senate Budget Committee staffer himself, told Fox News Digital.
"I think that she has more of a 'small-c' conservative approach to what is allowable. At the same time, a lot of what is considered to be allowable under reconciliation is dependent on estimates that are produced by the Congressional Budget Office or the joint tax committee."
When asked if any of the current public reconciliation plans could face issues with the parliamentarian, both people who spoke with Fox News Digital floated an accounting maneuver that would largely obscure the cost of permanently extending Trump's 2017 Tax Cuts and Jobs Act.
That scoring method, known as current policy baseline, would zero out the cost of extending the 2017 tax cuts by measuring it as an extension of the current economic conditions, rather than factoring in how much less the government is taking in via tax revenues with the cuts in effect.
Senate Republicans have signaled they believe they have the legal basis for moving forward with that calculation, however, without the parliamentarian's say.
"We think the law is very clear, and ultimately the budget committee chairman makes that determination," Senate Majority Leader John Thune, R-S.D., told reporters last month.
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The Senate GOP aide who spoke with Fox News Digital said, "If that were to have fallen out or just, you didn't know what was going to happen, that would just affect so many provisions in the bill."
"Because all of a sudden, you know, all these things start scoring [as an increase to the deficit]…and things become more problematic with your instructions," the former aide said.
Winfree, however, said Republicans have appeared to be mindful overall with how they have written the text so far.
"They've actually been pretty conservative in how they've approached the language," he said.
He said it was "possible some of the immigration provisions could get a second look," but that even then, he believed it would "ultimately be okay."
Republican leaders have said they hope to have a bill on Trump's desk by Fourth of July.
Fox News Digital reached out to the current Senate Majority Leader's office for comment.
