The White House and Congress are gearing up for a fierce battle over President Trump’s pivotal nomination to the Supreme Court, which he is expected to announce Tuesday.

Sen. Jeff Merkley Jeffrey (Jeff) Alan MerkleyThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Sunday shows - Trump team defends coronavirus response Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE (D-Ore.) turned up the temperature on Monday, circulating a petition that argues his colleagues should block any nominee from Trump given the Senate GOP’s decision to not grant a vote or hearing to Merrick Garland, whom then-President Obama nominated to the court last year.

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“This is the seat that [Senate Majority Leader] Mitch McConnell Addison (Mitch) Mitchell McConnellObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE [R-Ky.] and [his] team have stolen from President Obama,” he said in an email to supporters. “I won’t be complicit in this theft.”

A spokeswoman for Merkley confirmed that the Oregon Democrat will block any nominee besides Garland, who is not on Trump’s list of potential picks, from winning Senate approval by a simple majority vote.

Trump has vowed to appoint a conservative jurist, and Senate Democratic Leader Charles Schumer Chuck SchumerPelosi orders Capitol flags at half-staff to honor Ginsburg Ginsburg in statement before her death said she wished not to be replaced until next president is sworn in Democrats call for NRA Foundation to be prohibited from receiving donations from federal employees MORE (N.Y.) has threatened to block any nominee deemed outside the mainstream.

The pick will replace Antonin Scalia, the conservative justice who died in February 2016. Adding a conservative could give the right a working majority, though Justice Anthony Kennedy typically holds the court’s swing vote.

Only four filibusters have ever been launched against Supreme Court nominees, but the likelihood of a fifth is high given the tension surrounding the blocked Garland nomination.

Republicans hold 52 seats in the Senate. To defeat a filibuster, they would need eight Democrats to cross party lines.

The last filibuster against a Supreme Court nominee occurred when Democrats sought to block Samuel Alito’s nomination by President George W. Bush in 2006. It failed, and Alito was confirmed by a vote of 58-42.

Only one high court nominee, Abe Fortas, has been successfully filibustered. President Lyndon B. Johnson withdrew his nomination after the Senate voted against ending debate.

Merkley, one of his caucus’s most liberal senators and the only supporter in the Senate of Sen. Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE’s (I-Vt.) presidential campaign last year, isn’t alone.

Sen. Richard Blumenthal (D-Conn.) is also pledging to use the Senate’s procedural hurdles to try to block Trump’s nominee if the individual is an “extremist.”

“I want to fill [an] open seat, but I will oppose — and will actively use every legal tool to block — an extremist, unqualified nominee,” said Blumenthal, a member of the Judiciary Committee.

Republicans are returning fire, arguing Democrats are ignoring the will of voters who handed Republicans their first unified government in roughly a decade.

“I think if you’re a Senate Democrat, you’ve got to wonder whether or not you’re getting outside of Washington enough,” White House press secretary Sean Spicer told reporters Monday.

McConnell has noted that Republicans did not filibuster Obama’s two first-term nominees. McConnell said Trump should get the same treatment.

“We have every right to expect the same courtesy from today’s minority when we receive this nomination tomorrow,” he said from the Senate floor.

The GOP also could opt for the “nuclear option” by changing Senate rules to get rid of the 60-vote threshold for Supreme Court nominees, something Trump has said should be done if Democrats block his pick. McConnell has repeatedly signaled he does not want to take that step, most recently in an interview with The Hill on Friday.

Spicer declined on Monday to weigh in on whether the Senate should change the rules.

It’s not clear whether Democrats would be able to sustain a filibuster on any Trump pick.

Schumer’s office declined to comment on whether he would move to require 60 votes for Trump’s picks.

He added during an interview on NBC’s “Today” show Monday that Democrats weren’t looking for “payback” over Garland’s treatment.

Complicating the fight are the 10 Democrats up for reelection in 2018 in states Trump won.

The Senate Leadership Fund, which has ties to McConnell, questioned whether Sens. Joe Manchin Joseph (Joe) ManchinBiden promises Democratic senators help in battleground states Senate leaders quash talk of rank-and-file COVID-19 deal OVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' MORE (D-W.Va.), Heidi Heitkamp Mary (Heidi) Kathryn HeitkampCentrists, progressives rally around Harris pick for VP 70 former senators propose bipartisan caucus for incumbents Susan Collins set to play pivotal role in impeachment drama MORE (D-N.D.), Jon Tester Jonathan (Jon) TesterPence seeks to boost Daines in critical Montana Senate race This World Suicide Prevention Day, let's recommit to protecting the lives of our veterans Filibuster fight looms if Democrats retake Senate MORE (D-Mont.) or Claire McCaskill Claire Conner McCaskillDemocratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally Missouri county issues travel advisory for Lake of the Ozarks after Memorial Day parties MORE (D-Mo.), all up for reelection, would support Merkley’s filibuster.

The Judicial Crisis Network, a conservative group, plans to spend $10 million to confirm Trump’s nominee, while Tea Party Patriots plans to hold 1,000 house parties in the next 100 days to rally activists.

Carrie Severino, chief counsel and policy director of the Judicial Crisis Network, says her group will mount a pressure campaign targeting the 10 Democrats running for reelection in states that supported Trump.

“For the Democrats who are up for reelection in 2018, it’s going to mean choosing between the interests of their constituents and the interests of Democratic politicians,” she said.

On the left, organizers say hundreds of groups, including People for the American Way, the Alliance for Justice, MoveOn.org and the Leadership Conference on Civil and Human Rights, are planning to flood Senate offices with phone calls and constituent visits.

“There will be a wall of opposition senators are going to find among their own constituents,” said Ben Winkler, Washington director of MoveOn.org.

Liberal groups won’t disclose the size of their budgets and concede that conservative groups will likely outspend them, but they say the money can be matched by grassroots activism.

“We’re gearing up. We’re ready to fight,” said Marge Baker, executive director of People for the American Way. “It’s going to be big. I’ve been here 14 years. This is huge. Partly because the events of the past week have shown how important the courts are.”