The fight to replace retiring Justice Anthony Kennedy is expected to be the most expensive Supreme Court confirmation battle in history.

Conservative groups predict they will exceed their past expenditures over the summer and fall to boost President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE’s forthcoming nominee, who could change the ideological balance of the court for years to come.

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Liberal groups are also expected to spend freely and have warned that Trump’s pick could tip the scales against the Roe v. Wade decision that legalized abortion nationwide.

“I rank this as the most important I would’ve been through, largely because of the state of the country and the divisions that have been driven into this,” said Sen. Dianne Feinstein Dianne Emiel FeinsteinFeinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight Democrats shoot down talk of expanding Supreme Court Biden leads Trump by 12 points among Catholic voters: poll MORE (Calif.), the top Democrat on the Senate Judiciary Committee.

Feinstein joined the Senate in 1992 and has voted on seven different Supreme Court nominees going back to Ruth Bader Ginsberg in 1993.

Last year’s battle to confirm Trump’s first nominee to the court, Neil Gorsuch, is generally believed to have been the most expensive court fight in history, though it’s hard to know for sure because advocacy groups that report under 501(c) of the tax code don’t have to report all their expenditures.

“I would not be surprised at all if it not only set a record, but we saw far more spending than we saw in past Supreme Court battles,” said Robert Maguire, who tracks spending by political nonprofits at the Center for Responsive Politics.

“We’re seeing groups gear up faster than they have in the past,” he added. “These groups are well-funded. They can raise money for this, something that wealthy donors are very passionate about.

“They’re going to pour as much money as they can into this.”

Shortly after Kennedy announced his retirement on Wednesday, the conservative Judicial Crisis Network said it would spend at least $1 million on a national cable and digital advertising buy targeting Democrats up for reelection in states that Trump won in 2016.

Americans for Prosperity, another conservative group that serves as the political arm of the network founded by billionaire industrialists Charles and David Koch, also revealed Wednesday that it would spend more than $1 million on a campaign “to support a nominee in the mold of Neil Gorsuch.”

Both liberals and conservatives, however, expect a more intense fight this year because Kennedy — unlike the late Justice Antonin Scalia, whom Gorsuch replaced — often cast the deciding vote on major cases.

Republicans have a smaller majority in the Senate than they did when Gorsuch was confirmed in April of last year.

The GOP lost the Alabama Senate seat in a December special election, and Sen. John McCain John Sidney McCainThe Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' Cindy McCain: Trump allegedly calling war dead 'losers' was 'pretty much' last straw before Biden endorsement MORE (R-Ariz.), who is undergoing treatment for brain cancer, isn’t expected to return to Washington anytime soon.

With an effective majority of only 50 seats, Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellFEC flags McConnell campaign over suspected accounting errors Poll: 59 percent think president elected in November should name next Supreme Court justice Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ky.) cannot afford a single defection on Trump's next Supreme Court pick should Democrats remain unified in opposition.

The biggest spender in the Gorsuch debate was the Judicial Crisis Network, which spent $10 million to promote Trump’s first nominee and, before that, spent $7 million to support the blockade of then-President Obama’s nominee, Merrick Garland Merrick Brian GarlandPoll: 59 percent think president elected in November should name next Supreme Court justice Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' Chief justice honors Ginsburg: 'When she spoke, people listened' MORE, in 2016.

Carrie Severino, Judicial Crisis Network’s chief counsel and policy director, predicts the group will likely make an even bigger splash to get a judge similar to Gorsuch to fill the seat being vacated by Kennedy.

“I would certainly say it’s going to be at least $10 million,” she said. “This is going to be an even bigger fight and therefore I only anticipate the budget will grow.”

Other groups spent lavishly on Gorsuch as well. The National Rifle Association poured in $1 million to help him, while Americans for Prosperity waged a massive grass-roots campaign that included advocacy calls to more than 350,000 people and a direct-mail campaign in 12 key states.

Americans for Prosperity says it will likely do even more to ensure that a conservative judge replaces Kennedy.

“All indications are this is going to be a bigger fight than last time,” said Sarah Field, vice president of judicial strategy for the group.

“We have a different Senate than we did last time. There are a whole bunch of factors but certainly this is going to be bigger,” she added. “This is going to be an even bigger fight, an even bigger investment than it was with Justice Gorsuch.”

Conservatives enjoyed a major fundraising advantage during the last confirmation fight.

Nearly two months after Trump nominated Gorsuch, The Washington Post estimated that outside conservative groups outspent liberal groups by a 20-to-1 margin, citing a Republican estimate of ad purchases.

Liberal leaders think their supporters will be more energized this time around.

“There’s a lot more collective action going on right now in the country,” said Richard Trumka, president of the AFL-CIO, a labor union with 12.5 million members, who held a press conference Thursday on Capitol Hill to criticize a recent Supreme Court decision striking down requirements on government workers paying union fees.

He pointed to teachers going on strike around the country to demand better pay, the "Me Too" and Black Lives Matter movements.

“People are angry,” he said. “It’s going to be a lot easier to get people’s attention and then have them get the attention of elected leaders.”

He said labor is more organized than it has been in years and is ready to exert pressure on Congress ahead of the November midterm elections.

“We have our biggest member-to-member program we’ve ever planned. It’s the deepest and the broadest and it will be used against people that vote to hurt workers,” he said.

Trumka said he couldn’t put a dollar figure on the labor effort to influence the confirmation battle because it will be part of its broader communications work with members.

“We’ve integrated this into everything we’re doing. We’ve integrated it into our political program, we’ve integrated it into internal organizing,” he said.

Lee Saunders, the president of the American Federation of State, County and Municipal Employees, who also spoke to reporters in the Capitol, pointed to a rally that morning in front of the Supreme Court.

“The American public is fed up with going,” he said. “You’ve got so many movements coming together.

“The trick is to have the plan, have the strategy, work together very, very closely, channel that anger and frustration, and getting in the streets and making your voices heard and voting in November,” he added. “The Supreme Court piece is just one part of it.”

The Senate debate is likely to draw major spending on the left because many activists see the ideology of Kennedy’s successor as hugely significant on the future of abortion rights.

Kennedy joined the court’s four liberal justices in Whole Woman’s Health v. Hellerstedt decision against a corporate law that could have closed three-quarters of the abortion clinics in Texas.

NARAL Pro-Choice America, a leading abortion-rights group, has announced a 50-state strategy campaign to encourage people to take action to influence the court debate.

“Now we know there is a multimillion dollar campaign to make good on the promise Donald Trump made on the campaign trail to install a justice on the Court that is dedicated to overturning Roe v. Wade, criminalizing abortion, and punishing women. This is not a drill,” NARAL Pro-Choice America President Ilyse Hogue said in a statement.

Officials with the group declined to say whether it would launch a television and digital advertising campaign or how much it would spend.