Sen. Sheldon Whitehouse (D-R.I.) has emerged as the Democratic Party's leading voice on the courts amid President Trump's rapid success in filling the judiciary with conservative justices.

Democrats have historically struggled to match the GOP's intense focus on the courts. They also lack the network of well-funded legal advocacy groups that conservatives use to mobilize supporters.

But with the Supreme Court preparing to decide a slew of contentious cases in the coming weeks and the Senate entering another confirmation fight over a controversial judicial nominee, Whitehouse is offering a road map for Democrats to fight what they see as the conservatives' "capture" of the court system.

“I can't say enough about Sen. Whitehouse and his relentless pursuit of this area of captured courts,” Senate Minority Leader Charles Schumer (D-N.Y.) told reporters last week. “It's something many of us have known for a long time but it never seems to have broken through.”

Whitehouse views Trump’s success at reshaping the courts as part of the culmination of a decades-long effort by conservatives to bring the federal government in line with the interests of big businesses and wealthy political donors. One arm of that project, which Whitehouse argues may be its most successful, has been aimed at the courts, promoting judicial nominees and a legal philosophy that’s hostile to environmental regulations, labor unions and consumer protections.

“As a senator, I've seen how a small group of right-wing and corporate donor interests have polluted our politics with floods of anonymous money,” Whitehouse said in a written response to questions from The Hill. “Unfortunately these interests also recognized that controlling the courts is a smart way to rig government in their favor and achieve policy goals they could never get through Congress. Today, we’re seeing the payoff of that work.”

Since Trump took office, he has successfully appointed 198 judges to the federal bench, including two Supreme Court justices and 51 appellate court judges. A New York Times analysis in March found that all but eight of the appellate judges had ties to the Federalist Society, an influential group of lawyers and legal academics that preaches conservative principles like limited government.

The Federalist Society has major influence over the White House’s judicial nominations, with Trump saying that his shortlist of potential Supreme Court justices released during the 2016 campaign was vetted by the group.

“Our opponents of judicial nominees frequently claim the president has outsourced his selection of judges,” now-former White House counsel Don McGahn joked at a Federalist Society event in 2017. “That is completely false. I’ve been a member of the Federalist Society since law school. Still am. So, frankly, it seems like it’s been in-sourced.”

Brian Fallon, a former Schumer aide who founded the group Demand Justice to push Democrats toward focusing more on the courts, says Whitehouse has led the party in connecting the dots between the big-money conservative legal groups and the rightward tilt of the Supreme Court over the years, most recently with Senate Majority Leader Mitch McConnell (R-Ky.) and GOP senators confirming Trump’s nominees.

"Sheldon Whitehouse understands that Democrats can't play by an old rulebook that Republicans long ago tore up. He's also doing the hard, important work of taking on the infrastructure that turns big checks from corporate interests into pro-corporate Republican judges,” Fallon said. “He's the Federalist Society's biggest enemy in the Senate — which makes him a hero for everyone who cares about saving our courts from Trump and McConnell."

Whitehouse is an unlikely leader for his party on this issue, considering he’s the fourth most-senior Democrat on the Senate Judiciary Committee. He told The Hill that his experience as a federal prosecutor and state attorney general in Rhode Island prompted him to focus on the courts.

“I know how sick a litigator would feel to come before a judge who’ll rule against them based solely on the political, rather than the legal, merits of their position,” Whitehouse said.

The 64-year-old senator is known to weigh in on high-profile cases at the Supreme Court every year, submitting lengthy legal briefs aimed at countering the court’s rightward drift.

While it’s not unusual for a lawmaker to file “friend of the court” briefs, as they are otherwise known, Whitehouse has been relatively prolific when it comes to weighing in on high-profile cases — according to his office, he’s filed at least a dozen such briefs in the past three years.

That advocacy has made him a target for conservatives.

Last year, when he filed an amicus brief just before the Supreme Court agreed to hear its first major Second Amendment case in 10 years, Whitehouse accused the court and its five-member conservative majority of doing the Republican Party’s bidding in seeking to dismantle gun control laws.

He also cited public opinion polls showing a majority of Americans believe the court is influenced by politics and warned that undermining New York’s gun control law, in New York State Rifle & Pistol Association Inc. v. City of New York, would erode public trust in the institution.

“The Supreme Court is not well. And the people know it. Perhaps the Court can heal itself before the public demands it be ‘restructured in order to reduce the influence of politics,’ ” Whitehouse wrote, quoting a question from an opinion poll. “Particularly on the urgent issue of gun control, a nation desperately needs it to heal.”

The remark triggered a fierce backlash from conservatives, who accused Whitehouse of pushing “court packing” — adding seats to the court in order to flip the majority. The Wall Street Journal editorial board blasted the brief as “rank demagoguery,” and all 53 Republican senators signed a letter to the justices urging them “not to be cowed by the threats of opportunistic politicians.”

Whitehouse has responded by saying he does not support court packing, and instead favors transparency measures to require dark money groups to disclose their donors and identify who is funding the business-friendly groups filing amicus briefs in major cases.

“The best way to counter right-wing donors’ massive dark money machinery is to expose who’s behind it,” he told The Hill. “Dark money is the linchpin of the capture operation. When the public sees who’s behind the capture of their courts, a new trajectory can emerge.”

In recent months, Whitehouse has pushed for information from the Trump administration about the Federalist Society’s role in advising the president on judicial nominations and led lawmakers in calling on the judicial system to adopt a proposal that would ban sitting judges from associating with groups like the Federalist Society or the liberal American Constitution Society.

Those efforts have again put him in the crosshairs of the conservative legal movement he frequently speaks out against.

“On one level, it's almost conspiracy theory,” Carrie Severino, the president of the Judicial Crisis Network, said of Whitehouse’s criticisms of her group and other conservative ones.

She countered that progressives have plenty of legal groups — like the ACLU, NAACP and Public Citizen — and that they have dominated academic positions at law schools across the country.

“What the Federalist Society and the conservative legal movement had to struggle with early on was the fact that there was such a large network on the left, and one that had permeated completely into legal academies such that it was unheard of to even have any diversity of opinion,” Severino said.

Though none of Whitehouse’s major proposals have any likelihood of success while Republicans control the Senate and White House, his crusade has won praise from Democrats, especially at the leadership level.

Schumer last week joined Whitehouse and Sen. Debbie Stabenow (D-Mich.) in releasing a report on the GOP’s “capture” of the judiciary with the help of groups like the Federalist Society, arguing that it has led to major decisions undermining labor unions, voting rights and campaign finance limits. The minority leader also signed on to Whitehouse’s letter supporting the proposal that would ban judges from being Federalist Society members.

In their report from last week, the senators promised that Democrats would be further highlighting judiciary issues in the lead-up to Election Day.

“Americans have increasingly come to understand the culture of corruption that is undermining our politics,” they wrote. “Yet too few people realize that these same corrupting forces are now hard at work to influence and capture our courts. Over the coming months, Democrats in the Senate will work to change that.”