Stephen Miller’s Next Act Finds a Stage in the Courts

Mr. Miller, an architect of the last administration’s restrictive immigration policies and a leading backer of its socially conservative initiatives, is launching this week a new organization, America First Legal, to challenge Biden administration initiatives at odds with Trump-era priorities.

“Anything the president does that we believe to be illegal is fair game,” he said.

The group, Mr. Miller said, would tap into the expertise of Trump administration lawyers, work with Republican state attorneys general and partner with lawyers around the country who need legal and financial resources for their cases.

The group also has broader ambitions, Mr. Miller said, to eventually get involved in litigation that goes beyond the Biden administration, including to support police officers, go after big tech companies and take on other business interests whose positions run counter to those he embraced in the White House.

The conservative legal arsenal is hardly bare. Republicans, much as they did during the Obama administration, already have launched a series of challenges, including to Biden limits on oil-and-gas production, and Texas Attorney General Ken Paxton succeeded early in blocking Mr. Biden’s planned 100-day pause on deportations.

Mr. Miller said he comes to the new project after observing firsthand how relentless litigation from groups such as the American Civil Liberties Union can slow down a White House. When the Trump administration pursued a new initiative, he said, “we wouldn’t get just one lawsuit in one court, we’d get six lawsuits in six courts.”

“It was an extraordinarily effective tactic, and there’s no counterpoint to that on our side,” he said.

The 35-year-old Mr. Miller isn’t a lawyer, but a political operative who worked for conservative lawmakers including Sen. Jeff Sessions (R., Ala.) and Rep. Michele Bachmann (R., Minn.) before hitching his star to Mr. Trump’s 2016 presidential campaign. He said he left the White House believing “that the most important thing we could do as people who philosophically believe in traditional values, conservative values…was to develop and launch a conservative answer to the ACLU.”

Anthony Romero, executive director of the ACLU, suggested he was unfazed by that prospect. “Good luck to him pushing positions that he was unable to secure when he was sitting in the West Wing,” he said. “He’ll have a tough road to travel.”

America First Legal’s supporters include former White House chief of staff Mark Meadows and Matthew Whitaker, a former acting U.S. attorney general, both of whom will sit on the group’s board of directors. Mr. Miller has also received private encouragement from former Attorney General William Barr and anticipates public support from Mr. Trump.

“Conservatives and America First supporters badly need to catch up and turn the tables, which is why I applaud Stephen and Mark Meadows for rushing to fill this critical void,” Mr. Trump said in an emailed statement to The Wall Street Journal.

Mr. Miller declined to disclose his initial budget or fundraising so far, saying only that he had raised “a tidy sum of money” which would pay for initial staff and finance an early round of cases. Those funds have come from donors “who can write very large checks,” he said, but the group plans to begin soliciting small and medium-size donations soon.

A White House spokesman for President Biden declined to comment.

“You can anticipate an avalanche of challenges to what we see as an abdication of any semblance of the rule of law in this administration,” South Carolina Attorney General Alan Wilson said. “We’re all out here working together in tandem, and there’s a space out there for people like Stephen.”

Mr. Paxton said Mr. Miller already is deeply connected with Republican attorneys general around the country. “He’s going to be an invaluable resource for us to rely on,” he said.

There are many conservative public-interest groups in the legal world already, but they tend to focus on specific areas of the law, such as protecting religion in public life, opposing abortion or attacking economic regulation.

Mr. Miller said he wants to take a broader, more nimble approach and push for a maximum volume of cases. “Nobody has the attitude of, ‘Let’s find the weakest points and legally attack them relentlessly and as often—and everywhere—that we possibly can,’” he said.

Mr. Meadows said he anticipated the group would spend much of its time working behind the scenes, with “a stealth panel of lawyers who aren’t as interested in making headlines as putting limits on the executive overreach of the Biden administration. That’s hopefully going to be a hallmark of this group.”

Litigation has become a key feature of the modern presidency and was a central story line of Mr. Trump’s four years in office. The ACLU sued the administration 413 times. Democratic state attorneys general frequently sued the Trump administration; California’s attorney general, Xavier Becerra, now secretary of health and human services, alone sued the previous administration at least 100 times.

The administration saw an array of its plans blocked or stalled in the courts. The Supreme Court sometimes allowed its policies to be implemented but other times dealt a final blow, including to its efforts to add a U.S. citizenship question to the census and cancel an Obama-era program providing work permits and deportation protections to young immigrants.

The ACLU’s Mr. Romero said his organization sued the Trump administration “not because they were Republicans but because they were the worst administration in modern times on civil liberties and civil rights.”

“We purposely decided to carpet-bomb the administration on many of its policies,” he said. “That takes a certain type of firepower and knowledge and infrastructure that took 101 years to build.”

Mr. Romero said the Trump administration made part of the job easy “because they were overreaching and disregarded the plain language of statutes and legal precedent.”

During the Trump years, Republicans criticized left-leaning groups for pursuing nationwide injunctions in more liberal court jurisdictions, such as in Northern California, that put Trump policies on ice across the U.S.

Now, they will be looking to take the same approach—from courts that lean more conservative, a strategy Republicans have pursued before. Mr. Miller said his group already is working with a Texas lawyer to roll out a first batch of lawsuits there.

“We want to get the same injunctions, we absolutely do,” he said. “It would be unforgivable for us to say this will only be a tool that those on the left side of the spectrum use.”

Mr. Miller conceded it would take time for his group to scale up in terms of operations and resources. In addition to money, he will likely need some success in court to have staying power.

Mr. Trump’s campaign, for example, raised large sums of money to challenge the 2020 election results, but the many lawsuits he and his supporters filed were defeated in courts across the country, with judges quickly tossing out most cases.

“Motions to dismiss are not hard to file—and easy to lose,” Mr. Romero said.

—Jess Bravin contributed to this article.

Write to Brent Kendall at brent.kendall@wsj.com