WASHINGTON — The biggest legislative negotiation in years is taking place on Capitol Hill and at the White House, with key holdouts shuttling back and forth, lawmakers locked in intense private meetings and the news media providing minute-by-minute coverage of the developments.

And Republicans in the House and the Senate have absolutely nothing to do with any of it.

Sidelined by budget rules that give majority Democrats full control over the social safety net bill they are trying to push through, Republicans are strictly spectators as they revel in the internal Democratic disputes, snipe at the emerging legislation and game out how best to take advantage of the situation for next year’s crucial midterm elections.

Top Republican lawmakers who are usually mobbed by reporters walk unimpeded through the Capitol corridors while Democrats are chased down for any snippet of the current state of play. The lack of attention has not gone unnoticed.

“We’re a little bit surprised you’re even here today, because we know all the news is being made on the other side,” Senator Mitch McConnell, Republican of Kentucky and the minority leader, told reporters who showed up for his weekly news conference on Tuesday.

It is not an unprecedented situation. As recently as 2017, Republicans went it alone on their Trump-era tax cuts using the budget reconciliation process, which shields legislation from a filibuster, knowing that Democrats would not support the corporate tax breaks the G.O.P. was eagerly handing out. In 2009 and 2010, Democrats had substantial enough majorities in the Senate and the House that they could enact the Affordable Care Act on their own over universal Republican resistance.

Aware that Republicans would never support the kinds of social and climate programs they are trying to enact in the safety net legislation, Democrats are the ones using reconciliation this time. With the shoe on the other foot and with razor-thin Democratic majorities, the one-sided legislating has rendered Republicans — who make up exactly half of the Senate and almost half of the House — virtually irrelevant as Congress debates potentially momentous legislation expected to cost at least $1.5 trillion.

“It is really odd,” said Senator Lisa Murkowski of Alaska, who is among the few Republicans who occasionally join with Democrats on important legislation and who helped craft the bipartisan infrastructure bill awaiting a final vote in the House. “As somebody who is open to ideas from both sides and works on a lot of different initiatives with Democrats, to really not be involved or engaged in any aspect of it is just really odd.”

But there seems to be no fear of missing out among Republicans, given their hostility to the emerging domestic policy package, which — even in its scaled-back form as Democrats whittle it down to appease crucial centrists — would lead to a level of social spending that is anathema to G.O.P. lawmakers.

“They just have to satisfy their political base to the point where it gets pulled so far left,” Senator John Cornyn, Republican of Texas, said of the Democrats. “Obviously we don’t like being shut out of the policymaking, but that is the choice they made.”

In the meantime, Mr. Cornyn, like many of his Republican colleagues, has been captivated by the political and policy intrigue and numerous twists and turns as congressional Democrats and President Biden struggle to reach a deal.

“It is more fascinating than frustrating,” he said.

Their nonparticipation has freed up Republicans to unleash a political barrage against the Democratic legislation as various ideas rise and fall, providing multiple targets for the G.O.P.

Now, with Democrats promising an agreement is within reach, Republicans are increasingly taking to the floor and the other avenues available to them to assail the emerging plan.

In the Senate, Republicans active on energy and environmental issues blocked off a chunk of floor time on Wednesday to rip what they called the “reckless tax and spending spree” being pursued by Democrats. In the House, Representative Kevin McCarthy of California, the top Republican, has organized a series of round tables being digitally streamed and featuring lawmakers hammering on elements of the Democratic plan. Republicans are at the moment focused on the measure’s potential impact on home heating costs and gas prices, topics they believe can be political winners.

Mr. McConnell has been especially cutting about the Democratic plan in his daily floor remarks. On Tuesday, he described the expanded child tax credit Democrats see as one of its most popular components as “new monthly welfare deposits.” On Wednesday, he said climate change measures in the legislation amounted to “pure socialist wish fulfillment” and ridiculed Democrats for trying to rush provisions he said would drive up energy costs so Mr. Biden could celebrate them at a climate summit in Scotland on Sunday.

“Pain for the American people,” Mr. McConnell said, “so that President Biden can receive cheers from the crowd in Glasgow.”

He and other Republicans also went after the proposed tax on the unrealized gains on assets held by billionaires.

“Never before has that been attempted or tried or implemented in American history, where you would actually have a tax on income before people actually ever receive that income,” said Senator John Thune of South Dakota, the No. 2 Senate Republican.

Democrats welcomed the strong Republican defense of billionaires, noting that few policies poll higher than requiring the superrich who are able to escape hefty taxes to pay more.

“They are trotting out all sorts of excuses like it is untested,” said Senator Ron Wyden, Democrat of Oregon and a champion of the new tax as the chairman of the Finance Committee. “What I am waiting to see is if there will be a Republican elected official who will stand up and say it is OK for multibillionaires to pay little or no taxes for years on end.”

Like the rest of the country, congressional Republicans are waiting and watching to see if Democrats can pull off their highly difficult legislative feat. They hope not.

“We are not exactly cheering them on from the sidelines,” Mr. Cornyn said.