When an ailing Senator Dianne Feinstein requested in April to be quickly changed on the Judiciary Committee so Democrats may proceed the panel’s work with out her whereas she recuperated from shingles at residence in California, Republicans balked, blocking the substitution. Ms. Feinstein was compelled to return to Washington well before many close to her believed she was ready so her get together may proceed advancing President Biden’s judicial nominees.

Since then, a lingering query has hung over the Senate even because the 90-year-old Ms. Feinstein has refused to contemplate resigning earlier than the top of her time period in 2025: Could or would Republicans block Democrats from changing her on the committee if she did step apart, a departure that will open the door for an appointee chosen by the state’s Democratic governor to complete her time period?

No definitive reply has emerged — and the proposition might by no means be examined since Ms. Feinstein has mentioned she shouldn’t be going anyplace. But the query has main implications each for the Senate itself and for California politics.

Should Ms. Feinstein resign early, California’s governor would appoint a short lived senator who may then have a leg up within the hotly contested Democratic race to succeed her in January 2025. Gov. Gavin Newsom has mentioned he would title a Black lady, which may work to the drawback of different candidates within the race. The concept that an early departure by Ms. Feinstein may imperil Mr. Biden’s judicial nominees has been seen as but one more reason for her to remain.

Still, senators in each events counsel that that’s unlikely, and that Republicans may relent and permit an precise emptiness on the Judiciary Committee, versus a short lived opening, to be stuffed.

A chief purpose is that the Senate is an establishment closely certain by precedent — and a deep-seated reflex to do unto others as they did unto you. Blocking a committee alternative for a lawmaker who has been compelled to depart the Senate earlier than her time period is over is the kind of choice that might come again to hang-out Republicans, contemplating they’ve older members of their very own who may discover themselves in such circumstances.

Democrats would then have their alternative to refuse somebody a seat, and they might probably benefit from it in the event that they noticed it as justified retaliation. As in different circumstances, the tit-for-tat may rapidly escalate right into a brawl that will be pricey to each events.

Members on each side of the aisle say the distinction between vacating a seat quickly and changing a retiring member is critical, they usually consider that Democrats could be allowed to retain their majority on the influential panel.

“I can’t imagine that happening,” Senator John Cornyn of Texas, a senior Republican member of the Judiciary Committee, mentioned in regards to the prospect of stopping Democrats from seating a brand new member on the panel if Ms. Feinstein left. “I think that would be unsustainable.”

He added that the hypothesis on the matter “has to do with California politics and who wants to run to replace her.”

In an interview this 12 months on CNN, Senator Lindsey Graham of South Carolina, the senior Republican on the committee who formally objected to a short lived fill-in for Ms. Feinstein, additionally mentioned he “would be in the camp of replacing the person” if Ms. Feinstein or one other senator opened a slot by giving up a seat early.

Not everyone seems to be satisfied. Hillary Clinton, herself a former member of the Senate, helped reignite the difficulty final month when she mentioned in an interview with Time journal that she believed Republicans would block a alternative to thwart a push on judges.

“If we’re going to get judges confirmed, which is one of the most important continuing obligations that we have, then we cannot afford to have her seat vacant,” Mrs. Clinton mentioned.

And Senator Sheldon Whitehouse of Rhode Island, a senior Democrat on the committee, fanned the flames once more this month, saying on Twitter: “The fact is simple: if Senator Feinstein resigns, Mitch McConnell gets to decide whether Democrats have a Senate Judiciary majority.”

The suspicion that Republicans may impede a alternative is pushed not solely by the truth that they blocked a short lived substitute, but in addition by the truth that Senator Mitch McConnell, Republican of Kentucky and the minority chief, is hyper-focused on the make-up of the federal judiciary. He went as far as to dam Merrick B. Garland, who’s now the lawyer basic, from getting a listening to on his 2016 nomination to the Supreme Court by President Barack Obama for almost a 12 months, a place that many noticed as far outdoors Senate norms.

To Democrats, it isn’t a lot of a leap to assume that Mr. McConnell could be greater than keen to tie up the Judiciary Committee to decelerate affirmation of Mr. Biden’s judicial picks if the chance arose.

Mr. McConnell declined to reply questions on the subject, along with his workers saying that it was a hypothetical and that Ms. Feinstein remained within the Senate and voting. But the final sense amongst Republicans is that Mr. McConnell acknowledges that it could break with Senate conference to dam Democrats from filling a committee seat if a member left.

Some Democrats additionally assume it’s unlikely that Republicans would go that far.

“I may be naïve,” mentioned Senator Richard Blumenthal, Democrat of Connecticut and a member of the Judiciary Committee, “but I believe they would allow the Judiciary seat to be filled if it was a resignation as opposed to just an absence. I really think a resignation could lead to replacement very quickly.”

“I don’t think you can dismiss the idea of a resignation simply because of the fear that Republicans have been destructive,” he added. “In the long run, it would be self-destructive because they are going to encounter this problem as well.”

Senator Chuck Schumer, Democrat of New York and the majority chief, mentioned he was unsure what Republicans would do. But given their opposition to Mr. Biden’s judicial nominees, he steered they might probably make it troublesome simply to impede extra confirmations.

“It’s logical they would pull out all the stops,” he mentioned. “They might not stop it, but they could certainly slow it down.”

For her half, Ms. Feinstein has made it clear on repeated events that she doesn’t intend to depart earlier than the top of her time period, making the entire query moot.

Senator Richard J. Durbin, Democrat of Illinois and the chairman of the Judiciary Committee, additionally mentioned he didn’t know what Republicans would do. But he does know what he hopes Ms. Feinstein will do as he tries to maintain advancing judges.

“I would hope that she continues to show up when needed,” he mentioned. “And she’s been very good at that the last several weeks.”