Sen. Joe Manchin, D-W.V., has come out against adding more justices to the Supreme Court, even as some fellow Democrats contemplate the strategy to shift the balance on the court back toward the left.

Manchin, who is arguably the most conservative Democrat in the Senate and hails from a state that President Trump easily won in 2016, said Sunday that he would not support adding justices to the court because it wouldn't have bipartisan support.

“I'm not going to vote for anything that would cause, basically, not be able to work in a bipartisan way,” Manchin on CNN’s “State of the Union,” when asked about expanding the court.”

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“That is not something that I would support. I can't support that,” he added. “The whole premise of this Senate and this democracy experiment of ours is certain decency and social order that basically has been expected from us and especially from the Senate … now all of the sudden they're going to say, ‘Oh you don't have to talk anymore, you just have to have 51 votes and forget about the minority,’ well the minority has always played an important part in the Senate's proceedings.”

Some Democratic senators – even those who in the past were averse to increasing the nine-member court - said in the wake of Justice Ruth Bader Ginsburg's death that the Republican rush to fill the high court vacancy could be a breaking point.

Massachusetts Sen. Ed Markey said on Twitter that if Republicans don't allow the winner of the Nov. 3 presidential election to select the next justice, “we must abolish the filibuster and expand the Supreme Court.”

While some progressives are urging presidential nominee Joe Biden to embrace reforms including adding justices, he has so far resisted embracing such a major change.

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Biden, who ran a relatively centrist primary campaign and spent 36 years in the Senate, is concerned that such moves would worsen a particularly polarized moment in American history.

Another worry is that changing the size of the court for the first time in 150 years would come back to bite the Democrats, leading to further expansion when Republicans next control Congress and the White House. Faced with a 6-3 conservative court as the new year begins, Democrats would need to add four seats to overcome the Republicans' edge. With a 15-justice court, just two more additions by the Republicans would solidify their advantage.

If Democrats win control of the Senate in the November elections, they probably would need to get rid of the filibuster, the Senate rule that requires 60 votes rather than a simple majority for most legislation, before they could move on legislative changes that might include the size of the court.

The Associated Press contributed to this report.