Democratic nominee Joe Biden and running mate Kamala D. Harris are facing growing pressure to say whether they would “pack” the Supreme Court if the Republican-led Senate names Amy Coney Barrett to the bench.

Over the past few days, the question — from Republicans, debate moderators and reporters — has dogged the pair.

It came up again Thursday, when Biden was asked at a campaign stop in Phoenix if he would support expanding the Supreme Court beyond nine justices. Once again, Biden declined to answer.

“You will know my opinion on court-packing when the election is over,” Biden told reporters at Phoenix Sky Harbor International Airport. “The moment I answer that question, the headline in every one of your papers will be about that rather than focusing on what’s happening now. This election has begun. There’s never been a court appointment once the election has begun.”

The idea of adding additional justices to the Supreme Court has been floated for years, and it is not without historical precedent.

But it reentered the conversation in earnest after the death of Justice Ruth Bader Ginsburg. Although the Republican-controlled Senate refused to consider President Barack Obama’s nomination of Merrick Garland in 2016 — saying, at the time, that it would not be appropriate to name a new justice in an election year — Sen. Mitch McConnell (R-Ky.) and his allies have promised to confirm Barrett by Nov. 3.

If successful, Barrett would become the third Supreme Court justice appointed by President Trump and tilt the court 6 to 3 in conservatives’ favor.

In response, some Democrats have vowed to leave nothing off the proverbial table should the party take control of the White House and the Senate. “If [the Senate] holds a vote in 2020, we pack the court in 2021. It’s that simple,” Rep. Joe Kennedy (D-Mass.) tweeted in the wake of Ginsburg’s death. Around the same time, Senate Minority Leader Charles E. Schumer (D-N.Y.) hinted that he would not rule it out.

Republicans have seized on such proposals to paint Biden and Harris as norm-busting radicals who would certainly expand the court, presumably with liberal justices, if elected. During Wednesday night’s vice presidential debate, Vice President Pence repeatedly pressed Harris on whether she would support court-packing, and accused her of giving a “non-answer” before declaring his own conclusion.

“The American people deserve a straight answer,” Pence said. "And if you haven’t figured it out yet, the straight answer is they are going to pack the Supreme Court if they somehow win this election.”

The reality is less clear. During the Democratic primary, nearly a dozen contenders — including moderates, progressives and, notably, Harris — said they would be open to adding justices to overhaul the Supreme Court. “We are on the verge of a crisis of confidence in the Supreme Court,” Harris told Politico last March. “We have to take this challenge head on, and everything is on the table to do that.”

Biden, however, explicitly did not support expanding the court, saying it would further politicize the judicial branch. “No, I’m not prepared to go on and try to pack the court, because we’ll live to rue that day,” Biden told Iowa Starting Line last July. During a primary debate a few months later, he said he “would not get into” the idea.

“We add three justices; next time around, we lose control, they add three justices,” Biden said last October. "We begin to lose any credibility the court has at all.”

But as the nominee, Biden has become more circumspect, an implicit acknowledgement of the complicated political calculus. Acknowledging that he is open to the idea would give Republicans ammunition to gin up their base, while clearly coming out in opposition to court-packing could alienate the Democratic Party’s liberal base.

For weeks, Biden has dodged questions about hypothetical Supreme Court expansions when asked, saying the line of questioning could be used by Republicans as a distraction from the GOP’s efforts to jam a Supreme Court nomination through.

It “will shift the focus,” Biden told WBAY News late last month. “That’s what [Trump] wants. He never wants to talk about the issue at hand and he always tries to change the subject. … The discussion should be about why he is moving in a direction that’s totally inconsistent with what the founders wanted. The Constitution says voters get to pick a president who gets to make the pick and the Senate gets to decide.”

“We’re in the middle of the election right now,” he added. "You know, people are voting now. By the time this Supreme Court hearing would be held, if they hold one, it’s estimated 30 to 40 percent of American people already have voted. It is a fundamental breach of constitutional principle. It must stay on that and it shouldn’t happen.”