Washington(CNN) The idea that the Supreme Court should be increased beyond its current nine seats, popularly known as "packing the court," is drawing new, if still tepid, interest on the presidential campaign circuit and among liberal advocates.

Former Attorney General Eric Holder recently endorsed the idea and presidential candidate Pete Buttigieg, mayor of South Bend, Indiana, has in recent days been talking up proposals to expand the nine.

"What we need to do is stop the Supreme Court from sliding toward being viewed as a nakedly political institution. I'm for us contemplating whatever policy options will allow that to be possible," Buttigieg said at CNN's town hall in Austin, Texas, Sunday night, explaining a proposal that would increase the court to 15 justices.

Such court packing, recalling President Franklin Delano Roosevelt's ill-fated attempt to add justices in the 1930s, faces long odds. Congress has not changed the size of America's highest court in 150 years. And liberal advocates are themselves divided over whether it would be a good option for the country.

But the idea is not so easily dismissed as it might have been in earlier eras or even earlier months.

Leading proponents premise the notion on the belief that after Congress expands the number of justices, a new Democratic president would be able to appoint justices to counterbalance today's court, which has a 5-4 conservative majority.

"Court packing is integral to any effort to restore democracy," asserts Aaron Belkin, a San Francisco State University political science professor who is executive director of Pack the Courts, a group advocating an expanded bench. Belkin, backed by a board that includes some prominent law professors, insists that liberal legislative proposals, such as to counteract climate change or expand Medicare, must be accompanied by a plan to ensure that such initiatives would be upheld in court.

Belkin said Pack the Court has raised $500,000 to support its efforts to generate support among presidential candidates, including by working in the field in Iowa. Belkin said his group's recommendation is the addition of four more justices, appointed by the president to life-tenured seats.

Proponents have been motivated by President Donald Trump's broadscale attack on constitutional norms, as well as his speed in filling all level of federal courts. Yet, pending proposals could, conceivably, allow another Republican president to exert greater control of the Supreme Court.

And some liberal law professors and progressive advocates have been speaking out against on the idea on more fundamental grounds.

"Focusing on such futile ideas is a distraction from the disciplined political work progressives need to do to regain momentum in the war over the courts," said Simon Lazarus, a Washington lawyer who was a domestic policy staffer in the Jimmy Carter administration and more recently a senior counsel at the Constitutional Accountability Center. He said liberals should focus on encouraging their constituencies to make the judicial branch an election-issue priority as conservative Republicans and evangelical voters have for decades.

FDR's attempt to "pack" the high court came in the mid-1930s when a conservative-dominated Supreme Court was striking down his New Deal initiatives intended to help America cope with the Depression. The justices invalidated laws to bolster the economy and help workers, for example, with minimum-wage and maximum-hour standards.

To enhance the chance that his initiatives would be upheld, Roosevelt proposed -- after he had won reelection in November 1936 -- the appointment of a new justice for every sitting justice older than 70. (Six of the nine were then over 70.)

The public did not embrace the idea, and then-Chief Justice Charles Evans Hughes worked privately with members of Congress to stall legislation related to the additional seats. Equally important, the court soon became more receptive to FDR's New Deal. In spring 1937, for example, it upheld a minimum-wage law that was similar to a measure previously struck down and separately endorsed a new labor relations board. (Justice Owen Roberts' key vote for the Roosevelt administration became popularly known as "the switch in time that saved nine.")

In time, the more conservative justices began to retire, and Roosevelt had his chance to appoint his own justices.

Duke University law professor Neil Siegel, a board member of the American Constitution Society who has worked on Supreme Court nominations for Democratic senators, warned that court-packing proposals, if enacted, could further politicize the high court.

"Packing the court could substantially increase the public perception -- and, perhaps more importantly, the perception among the justices themselves -- that the court is partisan and political in just the way, and to the same extent, that Congress is."

The partisan view of the court, however, may already be established in the public's mind.

Chief Justice John Roberts has tried to counteract the view that the judiciary is just another political branch of government. Last November, after criticism from Trump about a ruling by, as Trump put it, an "Obama judge," Roberts responded with a rare rejoinder.

"We do not have Obama judges or Trump judges, Bush judges or Clinton judges," he said. "What we have is an extraordinary group of dedicated judges doing their level best to do equal right to those appearing before them."

It was plainly a message to Trump, but the chief justice, a student of history who also keeps an eye on what might lie ahead, may have been thinking about challenges across the ideological spectrum.

A new prominent supporter

Holder, who was President Barack Obama's attorney general, addressed court packing at Yale Law School last week, generating new, high-level attention on the long-odds topic.

The Yale Daily News reported that Holder, who is not running for president, told an audience that if he were president and Congress was majority Democratic, he would consider adding two more court seats to compensate for Mitch McConnell's "power-grabbing antics" that prevented Senate consideration of Obama nominee Merrick Garland.

His spokesman Patrick Rodenbush said on Monday that Holder would consider any expansion "a corrective."

Democrats remain angry over Senate Majority Leader McConnell's action in 2016 blocking consideration of Obama's choice of a successor to Supreme Court Justice Antonin Scalia.

Scalia died suddenly in February 2016. Obama nominated US Court of Appeals Judge Garland that March and for the remaining 10 months of Obama's tenure, McConnell impeded Senate consideration of any kind. After his election, Trump appointed Neil Gorsuch to the Scalia seat, and Gorsuch was confirmed by the Senate in April 2017.

In 2018, Trump replaced Justice Anthony Kennedy, a moderate conservative, with Brett Kavanaugh. Separately, Trump has been appointing record numbers of federal appeals court judges, assisted by Senate Republicans who have changed filibuster and other procedural rules to speed approval of nominees.

Among presidential candidates, Buttigieg has expressed the most notable openness to the idea of court packing. Yet he is apparently not committed to any single proposal.

"One of them involves having 15 instead of nine justices," he told CNN's Jake Tapper Sunday night, "but I'm not just talking about, suppose I get elected as president, putting on six justices that I think agree with me, and daring the next president who might be conservative to throw on a couple more. That's the last thing we want to do. What we need to do is stop every vacancy from becoming this apocalyptic ideological battle that harms the court and the country."

Buttigieg said he envisions, in one possibility, changing the structure of the court, so that 10 of the 15 would be appointed by Democratic and Republican presidents. "The other five can only be seated by a unanimous consent of the remaining 10," he said, which would mean they would have the respect of the others and "can be counted on to think for themselves."

Supreme Court justices are appointed for life, as are lower court judges, according to the terms of the US Constitution. Any change to that lifetime tenure and the Constitution would require ratification by three-fourths, 38, of the 50 states.

Congress, on the other hand, may alone alter the number of justices. Even though that path is theoretically easier than amending the Constitution, it has not been done since 1869, when Congress established the nine seats, after a low of five justices and a high of 10 in earlier decades.

Currently on the nine-member bench, five justices are Republican appointees who vote generally conservative; four are Democratic appointees who generally vote liberal. That 5-4 split has been the norm for decades, but with last year's retirement of Kennedy and appointment of Kavanaugh, who had a strong conservative record as a lower appeals court judge, that rift deepened significantly.