By KEVIN FREKING

WASHINGTON (AP) — An obscure but consequential bookkeeping matter has become the latest flashpoint in Congress as Republicans labor to enact President Donald Trump’s sprawling tax cut agenda.

Senate Republicans are looking to change how extending many of Trump’s 2017 tax cuts would be scored when it comes to future federal deficits. The Congressional Budget Office has projected that extending the cuts would increase deficits by nearly $4 trillion over the coming decade.

Democrats accuse Republicans of violating Senate norms with the move. Senate Democratic leader Chuck Schumer, D-N.Y., says Republicans are going “nuclear,” blowing up the institution’s rules.

The debate carries major ramifications for Trump’s agenda and the country at large, with policy decisions in the balance that could shape America’s economic and budgetary outlook for years to come.

So what is the dispute all about?

Why lawmakers keep talking about the baseline

Republicans are looking to draft their bill using a “baseline,” or starting point, that shows no impact on the deficit.

Such a baseline assumes that Trump’s 2017 tax cuts will continue regardless of their expiration date, essentially counting their renewal as cost-free. On top of that, Republicans are planning to go forward without a ruling from the Senate parliamentarian on whether the scoring change fits within the guidelines for passing tax cut bills with a simple majority.

“They are deciding that the way we’re going to do this is to break the Senate and make up our own rules,” Sen. Cory Booker, D-N.J., said as he spoke on the Senate floor for more than 25 hours to protest Trump’s agenda. “This is how they are going to get a bill through that gives trillions of dollars in tax cuts to the wealthiest in the country.”

The accounting change makes it easier for Republicans to make the tax cuts permanent as they try to muscle a bill over the finish line this year. But it also underscores how tax cuts — as well as spending — have historically taken precedence over deficit reduction when it comes to legislative priorities, leading to more government borrowing and a national debt now exceeding $36 trillion.

The arguments for and against the change

Some of the most powerful forces in Washington are arguing for the accounting change.

Scores of deep-pocketed trade and business groups say that creating a pathway for making the 2017 tax cuts permanent provides the certainty and stability companies need to drive growth and productivity.

“Americans should not have to worry about their tax relief expiring every few years,” said Senate Majority Leader John Thune, R-S.D.

Meanwhile, fiscal watchdogs are sounding the alarm.

“I think this should be rejected by any fiscally responsible member of Congress,” said Michael Peterson, chairman and CEO of the Peter G. Peterson Foundation, a debt watchdog group. “It’s a blatant attempt to get around one of the few rules we have that protects the next generation and our fiscal future.”

How it all relates to the Senate’s filibuster

Republicans are looking to pass Trump’s tax cut package with a simple majority, which is usually not possible in the Senate, where most legislation requires 60 votes to advance.

But the process for avoiding a Senate filibuster comes with certain rules, including it can’t increase the deficit beyond a specific timeframe, typically 10 years. Republicans chose to sunset large portions of the 2017 tax cuts after just eight years to comply with that requirement.

The Senate parliamentarian generally decides whether legislative proposals fit within the rules for legislation not subject to a filibuster. But in this case, Republicans argue that Senate Budget Committee Chairman Lindsey Graham, R-S.C., has the prerogative to decide which baseline is used to score the bill’s cost.

Schumer bristled at the GOP’s approach.

“By ignoring the parliamentarian, Republicans are going nuclear,” Schumer said Wednesday. “They’re trampling all over rules that have governed the Senate for decades in order to give massive tax breaks for their billionaire friends.”

The issue also came up at the White House when Trump met with Republican senators.

“We explained to him that we no longer need a ruling from the parliamentarian, that we can do it through the authority of the Budget chairman,” said Sen. John Kennedy, R-La. “We told him undoubtedly the Democrats will challenge it. We will win.”

Maya MacGuineas, president of the Committee for a Responsible Federal Budget, notes that under the usual process, lawmakers have to fully offset the cost of the tax cuts in the long term or the bill’s provisions will sunset. The scorekeeping change would free Congress of acknowledging the price tag of the proposed extension, she said, and would reduce the pressure to offset the extension’s cost.

“It’s an accounting gimmick that would make Enron executives blush,” she said.

A different approach in the House

House Republicans in their budget plan proceeded under the premise that the tax cuts do have a cost, which they attempted to partially offset with at least $2 trillion in spending cuts.

It’s unclear if House Republicans will go along with the Senate change. House Budget Committee Chairman Jodey Arrington of Texas has said he would be open to the Senate’s proposal if certain conditions are met.

“What I would hate to see happen is for a product to come from the Senate that has all the tax cuts that any Republican in the Senate could desire under any circumstance, but none of the hard decisions to rein in the spending that is driving us off a fiscal cliff,” Arrington said.

Critics of the scorekeeping change also warn that Republicans may not like the precedent they’ve created should Democrats take back the majority. Peterson called it a “foundational change” similar to doing away with the filibuster, “and setting a dangerous precedent that could be abused by both parties in the future.”

In the way that Republicans are looking to make temporary tax cuts permanent, he said, Democrats could work to make new spending permanent.

“Both of which would add materially to the debt and circumvent longstanding traditions and actual rules that are in the budget process today,” Peterson said.