It’s the accounting maneuver that could break the Senate, upend the federal budget process and explode the national debt.

That’s according to critics of a fiscal tactic that congressional Republicans are now seriously considering as they struggle to figure out how to deliver on all of President Donald Trump’s policy demands.

Adopting the “current policy baseline,” as it’s called, could be the only way for the GOP to make Trump’s 2017 tax cuts permanent and avoid painful cuts to federal programs, as well as pile on new income tax exemptions for tips, overtime and Social Security. Trump is expected to discuss the move with members of the tax-writing Senate Finance Committee at a White House meeting Thursday.

If lawmakers adopt the change, it would essentially make it appear as though extending current tax rates, set to expire at the end of the year, would cost nothing rather than the roughly $4 trillion over 10 years that nonpartisan scorekeepers estimate.

But while some Republicans argue that continuing current tax rates shouldn’t be counted toward the deficit, critics of the maneuver — including prominent GOP budget experts — say that it would be a recipe for disaster, a fiscal Pandora’s box that once opened could be used to forever excuse huge ongoing deficits.

“I would caution my friends, my Republican friends and senators up there, be careful about this,” said Bill Hoagland, the former GOP staff director for the Senate Budget Committee. “Someday you may be in the minority.”

The tactic is so tempting because it would solve a very difficult political problem for Republicans. Budget hawks in the House who do not want the party-line domestic policy bill adding to federal deficits want to ensure that planned tax cuts are closely tied to the amount of spending cuts Republicans can achieve.

Even then, the $4.5 trillion upper limit the House put on tax cuts does not leave enough room for a permanent extension of expiring tax cuts, in addition to all the other tax-related asks Trump has made.

For instance, adding on Trump’s other tax-related asks, such as income tax exemptions for overtime, tips and Social Security benefits, could add up to another $5 trillion, according to the nonpartisan Committee for a Responsible Federal Budget.

Critics say members of either party could use the maneuver to disguise trillions of spending through tax policies. Democrats argue that if Republicans move forward, they would be doing away with decades of precedent — and reneging on decades of anti-deficit rhetoric — to enact tax cuts for the wealthy.

Massachusetts Sen. Elizabeth Warren called it “magic math” in an interview and said going in that direction would end the congressional budget process as it has existed for more than 50 years.

“They can’t repeal the underlying reality, a $4.7 trillion giveaway to billionaires and giant corporations will cost $4.7 trillion,” she said, referring to how much the tax cut extensions are estimated to cost with interest.

Said Sen. Mark Warner (D-Va.), who signed onto a recent letter with Warren questioning the GOP’s strategy, “If this was done in the accounting world, you wouldn’t be an accountant for very long.”

Meanwhile, the leading advocate of moving to a current policy baseline, Senate Finance Chair Mike Crapo (R-Idaho), argued that it would rectify budget scoring rules that favor higher spending over keeping taxes low.

“If you’re not changing the tax code, you’re simply extending current policy, you are not increasing the deficit,” Crapo said on Fox Business in January. “We’ve got to get some kind of sensibility into the way that we score.”

Sen. John Kennedy (R-La.), a Budget Committee member, brushed off the idea that Republicans were undermining the budget procedures in place since 1974 — but also acknowledged that turnabout could be fair play when Democrats get their next governing trifecta.

“They will probably use current policy themselves in the future when they’re back in the majority,” he said.

Besides being controversial from an accounting perspective, the current policy baseline represents a major political gamble for Republicans, with the fate of potentially all of Trump’s tax agenda hanging in the balance.

That’s because the GOP might not know for weeks, if not months, if the maneuver will pass muster with the Senate’s parliamentarian. With a permanent extension of the expiring tax cuts moving toward the center of the Republican must-do list, an adverse ruling could create a huge hole in the GOP’s math.

“It would complicate making the tax cuts permanent,” said Sen. Lindsey Graham (R-S.C.), who chairs the Budget Committee.

That could create pressure for Republicans to overrule or even fire the parliamentarian — a move that would upend the delicate balance senators of both parties have adhered to for decades: Only bills that comply with strict fiscal rules aimed at reducing deficits can be exempted from the chamber’s 60-vote requirement for ending debate and moving to a final vote.

“As far as I’m concerned, that might as well give away the filibuster in the Senate,” Hoagland said.

Republicans, for their part, say they aren’t doing anything out of compliance with the longstanding budget rules. And there’s widespread skepticism inside the Senate GOP that they would ever vote to overrule the longtime parliamentarian, Elizabeth MacDonough.

We can say “it’s a $4 trillion deficit that we’re going to add into this, or we can say it’s current policy, but everyone knows it’s the exact same the next day,” said Sen. James Lankford (R-Okla.) in an interview. “So it’s nomenclature.”

Key GOP staff are already quietly meeting with the parliamentarian to try to get informal vibe checks on what she is thinking. Though senators won’t get a formal ruling until they go through what’s called a “Byrd bath” — when the reconciliation bill is vetted to make sure it complies with the rules that allow them to pass it by a simple majority — they can and frequently do have conversations with the parliamentarian’s office before that as they try to game out their procedural strategy.

“We think the law is pretty clear … but these things are all subject to discussion and arguments made in front of the parliamentarian,” Senate Majority Leader John Thune said in a brief interview, while cautioning that they were a long way away from that point.

But there’s skepticism from former longtime congressional staff and budget experts that the Senate GOP plan will fall within the rules of reconciliation. Sen. Jeff Merkley (D-Ore.), the top Democrat on the Budget Committee, predicted the parliamentarian won’t green-light the GOP strategy because it “seems like a pretty big stretch” of the rules.

George Callas of Arnold Ventures, who served as former Speaker Paul Ryan’s top tax aide during the drafting of the 2017 law, said adopting the current policy baseline would amount to a “huge gimmick.”

“My understanding is that the Senate parliamentarian gives a great deal of weight to the existing rules and the precedents and takes a skeptical look at just expedient reinterpretations of those rules for political reasons,” he said.