Less than 24 hours after Justice Anthony M. Kennedy announced his retirement from the Supreme Court, liberal advocacy group Demand Justice rallied in front of the court building Thursday with a string of Democratic lawmakers with a unified message: We will fight.

A professionally printed “Ditch the List” sign featuring President Donald Trump’s face hung on the podium, an expression of dissatisfaction with his list of 25 solidly conservative potential picks. Numerous Democratic senators also seized on the phrase as a hashtag on Twitter.

“We have to face a reality coming at us where we might lose some of the most precious ideals of our country,” New Jersey Sen. Cory Booker said Thursday. “I stand here to say, ‘This will not happen without a fight.’”

It was an opening scene in the political hurricane forming around Trump’s forthcoming pick to fill Kennedy’s vacancy on the bench, one that could ding the credibility of the Supreme Court and the Senate’s confirmation process, and will be shaped by competing outside groups on social media, advertisements against vulnerable lawmakers, and rallies.

Watch: Decoding the High Court Confirmation Process – 2 Things Trump Needs to Worry About

Delaware Democratic Sen. Chris Coons said Thursday he expects a “battle royale.” Through all the mounting political energy on both sides, one enduring fact remains about the political state of play: Democrats alone don’t have the votes to stop Trump’s second appointment to the high court, so they will pursue other strategies that for now appear unlikely to sway Trump or divide Senate Republicans.

But certain lawmakers are at the heart of the tug of war when the Republican advantage is so slim. Republican Sens. Susan Collins of Maine and Lisa Murkowski of Alaska might oppose a nominee who appears to eager to strike at access to abortion, while Democratic Sens. Joe Donnelly of Indiana, Heidi Heitkamp of North Dakota and Joe Manchin III of West Virginia are all in close races for re-election in states that went for Trump in 2016.

Those three Democrats voted for Trump’s first appointment of Justice Neil Gorsuch. Florida Democrat Bill Nelson is in a tight race. And there are questions about the votes of Arizona’s Republican senators, with John McCain missing votes for health reasons and Jeff Flake blocking appeals court judges to pressure leadership for a vote on an unrelated matter.

Outside groups on attack

Demand Justice, the group that held Thursday’s rally that included Booker and Sens. Kirsten Gillibrand of New York and Christopher S. Murphy of Connecticut, among others, is trying a mix of education and lobbying. They want to capture the energy of the successful grass roots on display on issues such as migrant family detentions and repealing the 2010 health care law.

The group launched in May to aggressively influence lawmakers and spark progressives in the fight over Trump’s nominees with a $10 million fundraising goal in the first year. Former Hillary Clinton spokesman Brian Fallon leads the group, which already ran an ad against the nomination of Thomas Farr to be a district judge in North Carolina. The Kennedy vacancy is a much bigger deal.

“This is definitely going to be about the organizing and the activism, and calling senators, and showing up at town halls, and making clear that we’re paying attention and we care more than we ever have before,” said Christopher Kang, a former White House aide who worked on President Barack Obama’s judicial nominations.

The group might struggle to match dollar for dollar one on the other side, the conservative Judicial Crisis Network. That group, which says it spent $7 million to help stop Obama’s nomination of Judge Merrick Garland to the Supreme Court and up to $10 million supporting Gorsuch’s confirmation, jumped back into the fray Wednesday.

The group announced a seven-figure national cable and digital ad buy called “#AnotherGreatJustice” that will target vulnerable Democrat incumbents. The first ad features black-and-white photos of Democratic senators including Minority Leader Charles E. Schumer of New York and Elizabeth Warren of Massachusetts.

“Like they did before, extremists will lie and attack the nominee, but don’t be fooled,” the ad says as the lawmakers’ faces flash on the screen. “President Trump’s list includes the best of the best, and with your help, America will get another star on the Supreme Court.”

A spokesman for the political advocacy group Americans for Prosperity told NPR on Wednesday that the Koch-related group is prepared to commit more than $1 million “to support a nominee in the mold of Gorsuch — someone who will interpret the law as written and not legislate from the bench.”

In January, the group announced it would focus on judicial nominations and “educate its activists on the importance of a fully-functioning judiciary and, when necessary, will bring the full force of its grassroots muscle to the fight by making calls, holding events, dropping mail, and running ads to advocate for the confirmation of nominees who will respect the rule of law.”

Democrats closing ranks

Among Democrats on the Senate Judiciary Committee, a few themes emerged Thursday for their opposition to a candidate to replace Kennedy, who wrote key opinions on women’s right to abortion and LGBT rights that they fear will be threatened by Trump’s pick.

The most aspirational came from Sens. Dianne Feinstein of California and Amy Klobuchar of Minnesota, who urged Trump to identify a strong consensus nominee who will not divide the country, and reach across the aisle for a nominee who would play a similar centrist role on the court as Kennedy.

“I hope when the president looks at this appointment — the tea leaves from my perspective don’t look good on this front, but — I hope he’s looking at someone who will fill that role and someone who will show independence in that role,” Klobuchar said at a committee meeting.

Feinstein and committee Democrats argue that Republicans set a new standard by blocking Garland during an election year, and he was “left to dangle in Senate uncertainty.” But that’s unlikely to persuade Judiciary Chairman Charles E. Grassley of Iowa and Senate Majority Leader Mitch McConnell, who already have said their standard was for a presidential election year.

Booker proposed Thursday that the committee should not consider a nominee from Trump until the completion of special counsel Robert S. Mueller III’s investigation into connections between the Trump campaign and Russian operatives during the 2016 election. He said it is a conflict of interest for Trump, a subject in that investigation, to appoint someone who could decide issues in Mueller probe.

All of this comes, of course, before Trump has named a nominee. And it comes as Democrats already criticize how Republicans have changed Senate rules and traditions to swiftly confirm Trump’s nominees to the nation’s district and appeals courts.

“I’m afraid some of these extreme nominees we’ve seen come before this committee from the Trump administration will be reflected in his Supreme Court nominee,” Senate Minority Whip Richard J. Durbin of Illinois told reporters Thursday. “In fairness to the president, and we should be fair, he has this decision to make first.”