Sen. Jeff Sessions was an instantly divisive figure when President-elect Donald Trump named him as his next attorney general: conservatives and immigration hardliners welcomed the choice, while civil-rights groups and Democrats spent the day attacking the pick, with Sen. Elizabeth Warren saying his selection would be a “compromise with racism,” and Sen. Cory Booker saying, “I am concerned that he possesses ideologies that are in conflict with basic tenets of the Justice Department’s mission.”

In part the critics’ focus was on controversial past comments by Sessions, such as accusations that he said the NAACP and American Civil Liberties Union were “un-American,” and joked that he thought the Ku Klux Klan was “OK, until I learned they smoked pot.” But much of the concern is what he’d actually do as AG: that he’d undermine civil rights protections, prosecute more undocumented immigrants and allow companies to go wild with mergers.

So what could he really do? Some cabinet-level jobs have limited power to affect the country, either because of their narrow mission or the slow rule-making processes needed to make major changes in public policy. Not so the Attorney General. Though sitting on top of the vast Department of Justice bureaucracy, the AG has wide discretion to shift American policy in huge ways simply by how he prioritizes its limited resources—which cases the office chooses to prosecute and which ones it lets go. It runs dozens of agencies, including the powerful FBI, DEA, and the immigration courts. And it also, insiders say, exerts huge influence on the White House’s own sense of its power.

"At every cabinet meeting, they are the person who everyone goes to and says what are range of options,” said a former Bush administration official. “Being able to cabin or expand the range of options available to the executive branch is a very powerful capability.”

How could Sessions leave his fingerprints on the country? POLITICO talked with former DOJ officials and experts in various issues over which the attorney general has significant sway. Here are seven areas where Sessions could most dramatically change public policy.

1. Immigration

The stakes are high for many undocumented immigrants, particularly those who become caught up in the criminal justice system. The Department of Justice has two distinct areas of power over immigration: prosecuting immigration violations and administering the immigration courts. It has considerable authority over the enforcement of immigration laws, such as illegal reentry into the U.S. and immigration fraud. For instance, under Obama, the DOJ worked with the Department of Homeland Security on a program called Operation Streamline which prosecuted immigrants caught illegally crossing the border, which carries stricter consequences than if those caught at the border had just been returned to the other side. This program, widely hated by immigration activists, was scaled back in recent years.

A different agency within the Justice Department adjudicates the appeals of immigration court rulings and its decisions set precedent for future cases. Those decisions can often be technical and deal with arcane areas of immigration law but they can often be life-or-death decisions for the appellants, such as in cases over asylum law. The attorney general can overturn any precedent decision by designating it for review, granting him a significant power to change immigration policy.

“The attorney general has tremendous authority over the enforcement of immigration law,” said David Leopold, an immigration lawyers based in Cleveland.

There’s no specific number of undocumented immigrants who may be at risk if Sessions, who is known as a hard-liner on immigration, is confirmed as attorney general. But it could be part of a broader crackdown on illegal immigration, fostering greater fear among undocumented immigrants and making it harder for asylum-seekers to stay in the country legally.

2. Surveillance

The Department of Justice is responsible for defending the government in all surveillance disputes, such as when Apple refused to help the FBI decrypt the iPhone owned by the attacker in the San Bernardino terrorist attack. It also is responsible for defending the government before the Foreign Intelligence Surveillance Court, which oversees national security surveillance. Those decisions will now fall to Sessions and the people he installs at DOJ.

As POLITICO reported earlier today, Sessions has supported allowing law enforcement wide range to access that data, criticizing Apple in the San Bernardino case and warning against any attempts to constrain the NSA. The technology industry is already worried about how he will handle surveillance programs. After the Snowden leaks, tech companies have become more hesitant to share data with the federal government and more willing to go to court to prevent law enforcement companies from accessing their customers’ data, such as email, without a warrant.

A Sessions-run DOJ that takes a tough line against tech companies could result in much more heated battles between the government and industry—and fewer privacy protections for everyday American.

3. Police misconduct

Under Obama, the Department of Justice has made it a priority to crack down on police misconduct. Some of that has come through grants to local law enforcement agencies to purchase body cameras and other tools and through a task force to improve policing tactics. But one major tactic to clean up police departments has been through investigations by the DOJ’s Civil Rights Division, either into specific incidents or broad examinations of police departments.

These investigations have uncovered clear cases of racist behavior and comments by police officers, shining a light on practices in places such as Baltimore and Ferguson, Missouri. Many black and Hispanic Americans in these cities saw the police more as a threat than a force for protection.

Whether a Sessions-run Justice Department will continue to prioritize investigations into police misconduct is unclear. Many conservatives and police departments have resented the investigations and deemed them an example of government of overreach; they will applaud Sessions if he chooses to limit those investigations. But for many minorities, DOJ investigations are often their last chance to reform law enforcement agencies and receive justice under law.

4. Voting rights

The Civil Rights Division is also responsible for enforcing the Voter Rights Act and other laws that protect the right to vote. The federal government’s power over voting rights was significantly curtailed by the 2013 Supreme Court decision that eliminated the requirement that certain states receive preclearance from the federal government to make changes to their voting laws. Since that ruling, many states have made major changes to their voting laws, instituting voter ID requirements and changing early voting rules, among other changes. The Justice Department has challenged many of these reforms in court.

That decision-making authority will now fall on Sessions, who has previously suggested that voting law changes, mainly in the South, were not intended to hurt minorities. But experts believe that laws that curtail early voting or require an ID to vote disproportionately affect African-Americans. The DOJ under Obama has acted as the last bulwark against such laws. For many minority citizens, their access to the ballot is only as strong as the willingness of the Justice Department to challenge voting laws in court.

5. Other civil rights issues

Beyond police misconduct and voting rights, the Justice Department enforces civil rights laws on a wide range of issues. Sessions could roll back rules preventing schools from excluding kids who are undocumented immigrants or upholding the rights of transgender students. These controversial measures last only as long as the leadership in the Department of Justice is committed to them. The same goes for enforcement of housing laws or discrimination against LGBT Americans.

For LGBT and minority Americans, Obama’s willingness to stretch his authority under civil rights statutes has earned them protections previously afforded to millions of Americans. But to critics, it’s been an example of Obama’s disregard for the rule of law and willingness to infringe on state’s rights.

6. Antitrust enforcement

The enforcement of antitrust laws is increasingly garnering attention in Washington, with lawmakers on both sides of the aisle expressing concern about concentration in different industries. The power to police such anti-competitive behavior falls to the antitrust division of the Department of Justice. Antitrust enforcement has recently become a higher priority for the Obama administration but whether it will continue under the Trump administration is unclear.

Trump has expressed skepticism at some mergers, such as the $85 billion deal between AT&T and Time Warner but his position appeared to be for personal reasons in that case. (He didn’t like CNN’s coverage of his campaign.) How Sessions will handle these cases is unclear. Businesses will like a softer-touch approach that allows them to merge without the DOJ trying to block it in court or requiring certain concessions. But in an increasingly consolidated economy, four years of lax antitrust enforcement could lead to reduced choices for consumers and higher prices.

7. Marijuana

Since marijuana is still federally illegal under the Controlled Substances Act, the attorney general has the power to decide whether to enforce federal law in states that have approved medical or recreational marijuana use. Under Obama, the DOJ has taken a hands-off approach and Trump appeared to agree with that policy during the campaign, saying that marijuana should be left up to the states. But the president-elect has also never shown a deep interest in drug policy while Sessions has been a forceful opponent of marijuana legalization, including saying that “good people don’t smoke marijuana.”

“[Sessions] has a wide variety of options when it comes to cracking down, if he chooses to do so,” said Erik Altieri, the executive director of NORML, a group that supports marijuana legalization. “That could range from simply raiding and shutting down state legal stores, bringing criminal penalties against the owners of those stores and it could be throwing up roadblocks when it comes to the implementation of these ballot initiatives.”

States such as Colorado and Washington have acted as guinea pigs for the rest of the country, implementing rules and regulations around recreational marijuana use, and more states are set to join them after voters approved ballot measures last week. Legitimate businesses are operating openly in the states. Sessions could shut down these businesses and enforce the federal law against marijuana use, pleasing anti-drug advocates—but likely infuriating many Americans in a nation that increasingly supports marijuana legalization.

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