When Donald J. Trump was running for president in 2016, he vowed to appoint Supreme Court justices who would vote to overturn Roe v. Wade. Three justices and six years later, he made good on that promise.
Mr. Trump also made a more general pledge during that campaign, about religion. At a Republican debate, a moderator asked whether he would “commit to voters tonight that religious liberty will be an absolute litmus test for anyone you appoint, not just to the Supreme Court, but to all courts.”
Mr. Trump said he would, and a new study has found that he largely delivered on that assurance, too. Mr. Trump’s appointees to the lower federal courts, the study found, voted in favor of claims of religious liberty more often than not only Democratic appointees and but also judges named by other Republican presidents.
There was an exception: Muslim plaintiffs fared worse before Trump appointees than before other judges.
“There seems to be a very big difference on how these cases come out, depending on the specific religion in question,” said Stephen J. Choi, a law professor at New York University, who conducted the study with Mitu Gulati of the University of Virginia and Eric A. Posner of the University of Chicago.
Another part of the study explored what was distinctive about Mr. Trump’s appointees to the lower courts, considering 807 judges named by seven presidents as of late 2020.
The study found, for instance, that judges named by Mr. Trump had “stronger or more numerous religious affiliations” with churches and other houses of worship, with religious schools, and with groups like Alliance Defending Freedom and First Liberty, which have won a series of major Supreme Court cases for conservative Christians.
Trump appointees were also much more likely to be members of the Federalist Society, the conservative legal group, than other Republican appointees: 56 percent versus 22 percent.
For appeals court nominations in the Trump administration, the study found that membership in the group was “virtually required,” with a rate of more than 88 percent, compared with 44 percent for other Republican appointees.
Mr. Trump made another pledge at another 2016 debate about the judges he would appoint. “They’ll respect the Second Amendment and what it stands for, what it represents,” he said.
The new study did not try to measure how Mr. Trump’s appointees voted in gun rights cases. But it did find that more than 9 percent of Trump appointees were members of the National Rifle Association, compared with less than 2 percent of other Republican appointees and less than 1 percent of Democratic appointees.
“In light of the polarizing nature of gun rights and the N.R.A.’s association with extreme views on gun ownership,” the study’s authors wrote, “jurists who seek a reputation for impartiality would normally want to avoid membership in the N.R.A.”
The study did document how Mr. Trump’s appointees voted in cases on claims of religious liberty, examining some 1,600 votes in more than 500 cases in the federal appeals courts from 2000 to 2022.
Trump appointees voted in favor of plaintiffs claiming that their right to free exercise of religion had been violated about 45 percent of the time, compared with 36 percent for other Republican appointees and 33 percent of Democratic appointees. The gap grew for cases that involved only Christians, to more than 56 percent, compared with 42 percent for other Republican appointees and 29 percent for Democratic ones.
And the numbers flipped when it came to Muslims, with Trump appointees at 19 percent, compared with 34 percent for other Republican appointees and 48 percent for Democratic ones.
“The pattern that emerges,” the study said, “is consistent with conventional wisdom: Democrats tend to protect minority religions, and Republicans tend to protect Christianity (and possibly Judaism).”
The study considered a common critique of Trump appointees: that they are less qualified than other judges. It found that the evidence did not support the charge, at least on average and at least as measured by the prestige of the law schools the judges attended, whether they had served as law clerks and ratings from the American Bar Association.
“We find little evidence that Trump judges break the historical pattern of judicial appointments,” the study’s authors wrote. “Women and minorities are less well represented among Trump judges than among Democratic judges, but that reflects a historical partisan difference; Trump judges do not differ much from Republican judges in this respect.”
“A few more Trump judges received top A.B.A. ratings, but not quite as many Trump judges attended top-10 law schools,” the study said. “Our view is that the data do not support the view that Trump’s judges were less qualified than judges appointed by other presidents.”
But the study’s main finding, on religion, was that Mr. Trump was true to his word.
“Trump is not known to be personally religious,” the study’s authors wrote, “but he appears to have believed that he could obtain votes by promising to appoint religious judges, and he kept his promise.”