Senate Democrats on Sunday accused Republicans of “going nuclear” to blow up the Senate rules so they can make President Trump’s 2017 tax cuts permanent.

The heated moment on the Senate floor came as Democrats made several parliamentary inquiries of the Senate’s presiding chair to lay the groundwork to challenge Budget Committee Chair Lindsey Graham’s (R-S.C.) use of a “current policy” budget baseline to score the extension of the 2017 tax cuts as not adding to the deficit.

“This is the nuclear option. It’s just hidden behind a whole lot of Washington, D.C., lingo,” Sen. Ron Wyden (D-Ore.), the ranking member of the Senate Finance Committee, declared on the Senate floor.

Republicans pushed back on that claim.

Graham argued that Democrats have previously used current-policy baselines to score bills. He pointed to former Senate Budget Committee Chair Kent Conrad’s (D-N.D.) use of a current-policy baseline to pass a farm bill.

Democrats, however, say that was done on a bipartisan basis and not for something as monumental as extending trillions of dollars’ worth of tax breaks.

Senate Finance Committee Chair Mike Crapo (R-Idaho) pointed out that former President Obama’s budget office in 2012 argued that the extension of the expiring Bush tax cuts should be scored as a continuation of current policy and as not adding to the deficit.

Democrats say that Congress has never before used a current-policy baseline to score tax cuts in a budget reconciliation package as not adding to future deficits.

They are pushing for the bill to be scored on a “current law” baseline.

Under current law, the 2017 Trump tax cuts would expire at the end of 2025.

The Congressional Budget Office (CBO) scores the extension of Trump tax cuts as adding to the deficit under a current-law baseline.

But under a current-policy baseline, which Republicans are using for the bill, the CBO scores the extension of the Trump tax cuts as not exceeding the bill’s reconciliation instructions or adding to federal deficits after 2034.

If extending the Trump tax cuts is scored as budget neutral, then the bill complies with the Senate’s Byrd Rule, which determines what legislation can pass the Senate with a simple-majority vote.

If Democrats win the procedural argument, the bill would have to be rewritten and the 2017 Trump tax cuts would have to be offset with huge additional spending cuts to comply with the Senate’s Byrd Rule.

If Republicans win the procedural argument, they will then be able to make the expiring portions of the 2017 Tax Cuts and Jobs Act permanent a major policy victory.

Wyden, Senate Democratic Leader Chuck Schumer (N.Y.) and other senior Democrats made parliamentarian inquiries on the floor Sunday afternoon to set up a later challenge to the Republican baseline.

Merkley asked the presiding chair, first-term Sen. Bernie Moreno (R-Ohio), if the House reconciliation bill used current law as the operative baseline when it was first laid before the Senate.

The chair answered “yes.”

Then Schumer asked if the Senate had ever used a baseline other than current law for a reconciliation measure, and the chair responded “no.”

Sen. Patty Murray (D-Wash.), the ranking member of the Appropriations Committee, asked if the nine titles of the Senate bill other than the Finance Committee’s portion used current-law baselines. Moreno answered “yes.”

Wyden then asked if the Finance title of the legislation relied on two different budgetary baselines, both current-law and current-policy baselines, and the chair acknowledged that is true.

Those answers prompted Murray, the longest-serving Democratic member of the Budget panel, to accuse Republicans of “ignoring precedent, process and the parliamentarian.”