In this Feb. 15, 2018, photo, Sen. Susan Collins, R-Maine and Sen. Lisa Murkowski, R-Alaska, left, are shown during a news conference at the Capitol in Washington. The Senate battle over Donald Trump’s new Supreme Court nominee is off to a fiery start _ even before the president makes his choice. Republican and Democratic leaders traded accusations and barbed comments Thursday on the new vacancy, abortion rights and the debate to come. (AP Photo/J. Scott Applewhite)

WASHINGTON — Liberal political strategists hope to block President Donald Trump’s next Supreme Court nominee by replaying a strategy they used to help defeat the Republican effort to repeal the Affordable Care Act last year.

The multimillion-dollar plan of advertising and grass-roots activism will focus heavily on convincing two Republican defenders of the ACA, Sens. Lisa Murkowski (Alaska) and Susan Collins (Maine), to buck the president again by denying his first choice to replace retiring Justice Anthony M. Kennedy. Trump plans to reveal his selection Monday.

One group, Demand Justice, plans to launch a $5 million campaign Thursday with ads in both senators’ states focused on the possibility that the next justice will provide the majority vote to allow states to ban abortion, overturning the 1973 decision in Roe v. Wade. NARAL Pro-Choice America announced plans Tuesday to take out full-page ads in four Maine newspapers highlighting the issue.

“We have a particular success with Murkowski and Collins, obviously, in the ACA fight,” said Brad Woodhouse, the executive director of Protect our Care, a liberal umbrella group that did organizing around the fights in 2017 over what had been President Barack Obama’s signature legislative achievement. “So we kind of understand how to do the work in those states.”

Republicans have 51 votes in the Senate and need 50 votes to confirm Trump’s nominee, assuming Vice President Mike Pence votes with them to break a tie. If Sen. John McCain, R-Ariz., does not return to vote after months of absence fighting cancer and Democrats hold together in opposition, a single Republican defection could sink the nominee.

The advertising and organizing effort will face a large counterattack from conservative groups. The Judicial Crisis Network has promised to undertake its own advertising campaign, focusing on Democratic senators in states that Trump won in 2016 who are facing reelection in the fall. The group spent about $10 million in an effort to ease the confirmation of Trump’s first Supreme Court pick, Neil Gorsuch, and has not yet announced a budget for a second nominee.

“I think it will not be an easy one for Democrats in those states to simply say, ‘I am going to tack hard left,’ ” said Carrie Severino, the chief counsel and policy director of the group. “We are not attacking Collins and Murkowski at all. They were supportive of Gorsuch and we think they will be supportive here.”

The Democrats’ targets include Sens. Joe Donnelly of Indiana, Joe Manchin III of West Virginia and Heidi Heitkamp of North Dakota, all of whom voted for Gorsuch.

The liberal strategy, which employs multiple staff members in each state, will include generating letters to the editor, sending people to the senators’ events and organizing phone calls to their offices.

The groups plan to argue that any Trump nominee from his preselected list would be a vote on the high court that will again allow abortion to be outlawed in every state and undo the ACA’s mandate that health insurers not discriminate against people with preexisting conditions.

“We have had support in the past from Senators Collins and Murkowski around the defunding of Planned Parenthood, around the protection of Roe v. Wade, and we believe that is a very important piece of this puzzle,” said Dawn Laguens, executive vice president of Planned Parenthood.

The liberal groups also plan to focus advertising and organizing on the states of the three Democratic senators who voted for Gorsuch. All three come from states where opposition to abortion is strong, and all face tough reelection fights this fall.

Liberals hope that concern about the ACA proves decisive with these senators as well. Demand Justice, an umbrella group that includes planned Parenthood and NARAL, will start airing ads Tuesday in all three of those states, arguing that Trump’s pick will determine whether insurance companies can discriminate against people with preexisting medical conditions.

The Justice Department joined a federal lawsuit in June to argue that the recent legislative repeal of the ACA’s individual mandate invalidates provisions of the law that ban insurers from charging more or denying coverage to people with preexisting conditions. That case could eventually reach the Supreme Court, where the last decision to let ACA stand, in 2012, came on a 5-to-4 vote, with Chief Justice John Roberts Jr. joining more liberal justices to protect the law.

One Nation, the public policy arm of the main Republican Senate advertising effort, Senate Majority PAC, also has announced plans to run spots against vulnerable Democratic senators in states that Trump won, though no budget has been made public.

“Will Joe Donnelly cave to the extreme left?” ran the tagline of one digital ad that One Nation posted last week.

Antiabortion groups also plan to organize in key states to pressure Democratic senators. The Susan B. Anthony List has 104 canvassers in Indiana, who have been going door to door to organize opposition to Donnelly.

“The pro-life movement is strongest when we are talking to them one-to-one,” said Mallory Quigley, a spokeswoman for the group.

Donnelly, who opposes abortion except in cases of rape, incest or to save the life of the mother, told the Indianapolis Star that it was too soon to say how he would vote on the nominee, while declining to say whether Roe should be overturned. “It’s the law of the land,” he said last week.

Manchin, who opposes abortion with the same exceptions as Donnelly, suggested in a radio interview Friday that Trump should avoid picking a justice who will overturn Roe.

“If he picks somebody that’s hardcore on Roe v. Wade or that hardcore on repealing health care, that’s a bigger lift,” Manchin said.

Heitkamp, who has argued that reproductive decisions should be left to a woman, her family and her doctor, does support a ban on federal funding of abortion in most cases. And she said she wants to do a “thorough vetting” of the president’s nominee before making a decision.

At the core of the liberal argument is the idea that any of the president’s nominees will be tainted if they come from a list he announced during the campaign. Trump also announced during the campaign that if he put two or three justices on the court, an overturn of Roe “will happen automatically, in my opinion.”

“Our point to Susan Collins is stop going around and pretending that there is some magic question that is going to give you legitimate reassurance [that the nominee will protect Roe],” said Brian Fallon, who is leading Demand Justice. “If they came from the list, it’s fruit of the poisonous tree.”

Collins has suggested that she has a different view. “I would not support a nominee who demonstrated hostility to Roe v. Wade,” she told CNN’s “State of the Union” on Sunday. But she also has said she has not ruled out voting for someone from Trump’s list, saying that although there are some she would not support, she first wants to hear their views on upholding precedent.

During the debate last year over the ACA, Collins made clear her objections to blocking federal funds for Planned Parenthood, which other Republicans had inserted as part of an effort to weaken the organization, a major provider of abortion services.

Murkowski also said she was committed to protecting continued funding of the group. Since Kennedy announced his retirement, she has called for “exacting scrutiny” of his replacement. “His retirement is a historic moment for the court because he was the swing vote in so many decisions of great consequence,” she said in a statement.

The fight for the favor of individual senators will take place amid a much broader effort by Democrats and Republicans alike to energize voters around the confirmation process for the nominee. The Alliance for Justice, a liberal group that focuses on Supreme Court nomination fights and vetting, plans to elevate the nominee’s record on federal regulatory law as part of an attempt to raise civil rights, labor and environmental issues.

Underlying it all is an awareness that the political environment is combustible and unpredictable. Nan Aron, the founder and president of the Alliance for Justice, cited past court nominee fights as instructive, noting that successful opposition to conservative Supreme Court nominee Robert Bork in 1987 led to the appointment of a moderate Kennedy.

“Everyone knows what is at stake this time,” she said. “As the fight to save the ACA demonstrated, when people are galvanized enough to pressure Democrats and Republicans, you can have an effect.”