FILE PHOTO: U.S. Supreme Court Chief Justice John Roberts delivers remarks at The American Law Institute?s 2023 Annual Dinner at the National Building Museum in Washington, D.C., U.S., May 23, 2023. REUTERS/Sarah Silbiger/File Photo

(Reuters) -John Roberts has served for two decades as the chief justice of the United States, a time when the Supreme Court has moved American law dramatically to the right.

Here is a look in chronological order at a dozen instrumental decisions by the court since Roberts, 70, was sworn in as the leader of the top U.S. judicial body on September 29, 2005.

DISTRICT OF COLUMBIA V. HELLER (2008)

The court decided that Americans have a right under the U.S. Constitution's Second Amendment to possess firearms in their homes in a ruling expanding gun rights. The 5-4 decision, written by Justice Antonin Scalia and powered by the conservative justices, overturned the District of Columbia's ban on handguns, a measure intended to combat firearms violence. Scalia rejected the view that the Second Amendment, which protects the right to keep and bear arms, applies only to gun ownership in connection with serving in what the provision refers to as a "well-regulated militia." The court in 2010 and 2022 delivered rulings that further widened gun rights.

CITIZENS UNITED V. FEDERAL ELECTION COMMISSION (2010)

The court, citing free speech rights under the Constitution's First Amendment, ruled that the government may not restrict political spending by corporations in elections. The 5-4 decision, authored by Justice Anthony Kennedy and joined by the court's conservatives, invalidated longstanding campaign finance limits and let corporations and other outside groups such as labor unions spend unlimited sums of money on elections. The court overturned two of its own precedents, from 1990 and 2003. The decision led to huge increases in political spending from outside groups and boosted the influence of wealthy donors, corporations and special interest groups. Kennedy wrote, "If the First Amendment has any force, it prohibits Congress from fining or jailing citizens, or associations of citizens, for simply engaging in political speech."

NATIONAL FEDERATION OF INDEPENDENT BUSINESS V. SEBELIUS (2012)

The court upheld the legality of the 2010 Affordable Care Act, a law passed by Congress that enabled millions of previously uninsured Americans to gain access to health coverage. The law, known as Obamacare, was President Barack Obama's signature domestic policy achievement. Roberts wrote the 5-4 decision, joining the court's four liberal justices. Roberts wrote that the law's mandate that most Americans obtain insurance or pay a penalty was allowed by the power of Congress to levy taxes as set out by the Constitution. "Because the Constitution permits such a tax, it is not our role to forbid it, or to pass upon its wisdom or fairness," Roberts wrote. The court upheld Obamacare in subsequent decisions as well amid further legal challenges.

SHELBY COUNTY V. HOLDER (2013)

The court ended the requirement for U.S. states with a history of racial discrimination to receive federal approval before changing their voting laws. In doing so, it gutted a core part of the landmark 1965 Voting Rights Act, which prohibited racial discrimination in voting. The 5-4 ruling, authored by Roberts and powered by the court's conservatives, found that Congress used outdated facts in continuing to force nine states, mainly in the South, to get federal approval for voting rule changes affecting Black people and other minorities. "Our country has changed, and while any racial discrimination in voting is too much, Congress must ensure that the legislation it passes to remedy that problem speaks to current conditions," Roberts wrote.

OBERGEFELL V. HODGES (2015)

The court recognized a constitutional right for same-sex couples to wed, legalizing gay marriage nationwide. The court ruled 5-4, with Kennedy joining its four liberal members, that the Constitution's guarantees of due process and equal protection mean that states cannot ban same-sex marriages. Kennedy wrote that gay people intending to marry "ask for equal dignity in the eyes of the law. The Constitution grants them that right." Kennedy added, "Without the recognition, stability and predictability marriage offers, their children suffer the stigma of knowing their families are somehow lesser." Roberts dissented. "Just who do we think we are?" Roberts wrote, calling the decision "an act of law, not legal judgment."

BOSTOCK V. CLAYTON COUNTY (2020)

The court ruled that a federal law barring workplace discrimination protects gay and transgender employees. Two conservative justices joined the court's four liberals: Roberts and Neil Gorsuch, who wrote the ruling. The court decided that gay and transgender people are protected under Title VII of the Civil Rights Act of 1964, which bars employers from discriminating against employees on the basis of sex as well as race, color, national origin and religion.

DOBBS V. JACKSON WOMEN'S HEALTH ORGANIZATION (2022)

The court overturned its 1973 Roe v. Wade ruling that had recognized a woman's constitutional right to an abortion. The court, in a 6-3 ruling written by Justice Samuel Alito and powered by its conservative majority, upheld a Mississippi law that banned abortion after 15 weeks of pregnancy. The vote was 5-4 to overturn Roe, with Roberts writing separately to say he would have upheld the law without erasing the Roe precedent. The ruling led a series of states to ban or restrict abortion. "Roe was egregiously wrong from the start. Its reasoning was exceptionally weak, and the decision has had damaging consequences," Alito wrote.

KENNEDY V. BREMERTON SCHOOL DISTRICT (2022)

The court ruled that a Washington state public school district violated the rights of a Christian high school football coach who was suspended for refusing to stop leading prayers with players on the field after games. It was one of multiple rulings by the Roberts Court expanding religious rights. Broadening the religious rights of government employees, the justices sided with the coach. The 6-3 ruling, authored by Justice Neil Gorsuch and powered by the court's conservatives, held that the coach's actions were protected by his rights under the First Amendment, which safeguards free speech and religious expression.

STUDENTS FOR FAIR ADMISSIONS V. HARVARD (2023)

STUDENTS FOR FAIR ADMISSIONS V. UNIVERSITY OF NORTH CAROLINA (2023)

The court struck down race-conscious admissions programs at Harvard University and the University of North Carolina, rejecting affirmative action policies long used to raise the number of Black, Hispanic and other underrepresented minority students on American campuses. Roberts wrote that student admissions programs that consider an applicant's race in ways like Harvard and UNC did violate the Constitution's promise of equal protection. The rulings, 6-3 against UNC and 6-2 against Harvard, were powered by the court's conservatives. Roberts wrote that a student "must be treated based on his or her experiences as an individual not on the basis of race."

LOPER BRIGHT ENTERPRISES V. RAIMONDO (2024)

The court dealt a major blow to federal regulatory power by overturning a 1984 precedent that had given deference to government agencies in interpreting laws they administer. The 6-3 decision, authored by Roberts, was one of multiple rulings powered by the conservative justices that hemmed in the authority of federal agencies. The precedent that was overturned, involving oil company Chevron, had called for judges to defer to reasonable federal agency interpretations of U.S. laws deemed to be ambiguous - a doctrine called "Chevron deference." Roberts wrote, "Courts must exercise their independent judgment in deciding whether an agency has acted within its statutory authority."

TRUMP V. UNITED STATES (2024)

The court ruled in favor of Donald Trump in deciding that presidents have immunity from prosecution for official actions taken in office. Roberts wrote the 6-3 ruling, joined by the court's other conservatives. Trump, while running to regain the presidency, had challenged a federal indictment concerning his actions aimed at overturning his 2020 election loss to Democrat Joe Biden. In recognizing broad immunity for Trump, Roberts cited the need for a president to "execute the duties of his office fearlessly and fairly" without the threat of prosecution. Roberts wrote that such immunity was required in light of the U.S. constitutional structure separating powers among the government's executive, legislative and judicial branches. The charges against Trump at issue in the case were later dropped, and he won the 2024 election.

UNITED STATES V. SKRMETTI (2025)

The court upheld Tennessee's ban on gender-affirming medical care for transgender minors. The 6-3 ruling, authored by Roberts and powered by the conservative justices, concluded that the ban did not violate the Constitution's equal protection language. Tennessee's law barred medical treatments such as puberty blockers and hormones for people under age 18 experiencing gender dysphoria, the clinical diagnosis for significant distress that can result from an incongruence between a person's gender identity and sex at birth. Roberts wrote, "Tennessee concluded that there is an ongoing debate among medical experts regarding the risks and benefits associated with administering puberty blockers and hormones to treat gender dysphoria, gender identity disorder and gender incongruence."

(Compiled by Jan Wolfe in Washington; Editing by Will Dunham)