Privacy advocates are deeply worried about how President-elect Donald Trump will use the investigative and surveillance capabilities of the Justice Department, the FBI and the National Security Agency.

One fear is that he will skirt the law to order surveillance of critics and political opponents. A broader worry is that he will use his authority under existing laws to expand the scope of domestic spying. In either case, there are warning signs.

Privacy people would probably worry that any new president might act to expand surveillance. But they are much more frightened by Trump, who has frequently vowed to act on his own authority, to punish critics and rivals and to ignore constitutional rights. This suggests that he could greatly expand surveillance and use it in unorthodox ways.

In some areas, he can expand surveillance without the approval of Congress or the courts. Such action could sharply curtail privacy without public debate or accountability. Presidents have a great deal of unilateral power over surveillance. Indeed, President Obama’s attorney general and director of national intelligence have imposed many of the current restrictions on FBI and NSA practices.

This makes them relatively easy to overturn. Trump could issue directives to his appointees to weaken or abandon those restrictions. For example, he could make it easier for FBI agents to seize and stockpile the personal records of Americans and to obtain the phone records of journalists. He could also give federal criminal investigators even greater access to the troves of data collected, without warrants, by the NSA. But because many details of surveillance practices and restrictions are secret, we don’t know exactly what he could do.

If Trump were to remove restraints on investigators or authorize new surveillance programs, the public wouldn’t necessarily hear about it. Presidents can issue classified orders to change the rules for domestic spying, knowing that the other branches of government are unlikely to push back publicly even if the orders violate statutes. As the Supreme Court has repeatedly held, presidents have the final say over public disclosure of national security information. Opponents usually cannot criticize classified rules without illegally revealing them.

However, there are warning signs that might help the public figure out that the Trump administration is unilaterally altering surveillance policies. Four kinds of signs are particularly important.

Efforts to silence privacy watchdogs

Several executive-branch agencies conduct oversight of terrorism investigations. Whom Trump selects to lead these agencies will tell us a lot about his views on protecting privacy.

The most important of these watchdogs is the Privacy and Civil Liberties Oversight Board — an independent agency that assesses whether surveillance activities undermine constitutional protections. For example, after the intelligence leaks by Edward Snowden, the board released two major reports (see here and here) that sharply criticized the NSA’s bulk collection programs.

Along with a small staff, the PCLOB has five presidential appointees: a full-time chairman and four part-time members, serving fixed terms and not removable by the president. Under normal circumstances, it would take Trump a number of years to replace Obama’s appointees on the board. But for several reasons, including an early departure, there will be two vacancies as soon as he takes office, and a third position will open up shortly after. We can watch to see if Trump leaves these positions vacant — which would prevent the board from having a quorum to issue reports. Alternatively, he could pack the agency with security hard-liners who would not make trouble over privacy concerns.

Apart from appointments, Trump will have other opportunities to weaken executive-branch agencies that have privacy mandates. Most other watchdog agencies lack the PCLOB’s independence. With an executive order, President George W. Bush virtually eliminated the core responsibilities of the President’s Intelligence Oversight Board.

If Trump moves to weaken watchdog agencies over the next year or two, it will indicate that he doesn’t want to be held accountable for his surveillance policies.

Whether public advocates appear before the FISA Court

The activities of the Foreign Intelligence Surveillance Court — a panel that authorizes domestic spying — may also tell us whether Trump is trying to expand investigative powers.

During the Bush presidency, the FISA Court secretly approved many of the NSA’s most controversial programs — including the blanket collection of phone and Internet metadata. Leaks by Snowden revealed that the court issued these decisions on shaky legal grounds, without considering privacy interests. To ensure more balanced deliberation, Congress in the 2015 USA Freedom Act established an official role of public advocate for the court. Instead of hearing only from Justice Department lawyers, FISA judges in important cases are now supposed to consult a public advocate and consider legal objections to enhanced surveillance.

To date, the FISA Court has consulted a public advocate in only one reported case. If we soon see public advocates appearing frequently before the court, we can infer that the Trump administration is pushing for broad new surveillance powers.

But we cannot count on seeing this tip-off. Under the same law, the director of national intelligence decides whether to inform the public about FISA Court cases. The next director may withhold information on hearings and conceal the activities of public advocates.

Warnings by congressional critics of domestic spying

If the Trump administration secretly adopts surveillance policies that appear to violate existing law, we may see members of the House and Senate Intelligence committees raising red flags.

Well before the Snowden leaks, several members of Congress claimed that the Bush and Obama administrations were using secret interpretations of the Patriot Act to justify intrusive domestic surveillance. They hinted at the existence of the metadata programs. In a 23-minute floor speech in 2011, Sen. Ron Wyden (D-Ore.) strongly suggested that the NSA was conducting mass warrantless surveillance in the United States.

These warnings, largely overlooked at the time, were later confirmed by the Snowden revelations. We now know that we should take Wyden and his congressional colleagues seriously if they complain about investigative abuse, even if they offer few details and no evidence.

As with watchdog agencies, however, the Trump administration will have means to hamper oversight by Congress. At the extreme, it could decide not to tell lawmakers about new eavesdropping programs. Although illegal, the stealth strategy has ample precedent.

More likely, the administration could meet its legal obligation to inform Congress, while minimizing the risk of opposition, by briefing only the congressional and intelligence committee leadership — the so-called Gang of Eight. So far, the Gang of Eight has dutifully kept quiet about potentially controversial intelligence practices. By either total secrecy or these leadership-only briefings, the administration could keep aggressive congressional critics such as Wyden in the dark about possible investigative abuses.

Leaks and whistleblowers

The last-ditch means for the public to learn about expanding surveillance is through leaks or whistleblowing by members of the intelligence community. If the administration ordered baseless investigations of its political opponents, for example, at least some federal agents would probably resist. The FBI today enjoys a high level of bureaucratic autonomy. Despite its much-criticized interference in the 2016 presidential race, it is unlikely to conduct politically motivated investigations for the White House.

But we shouldn’t rely too heavily on leaks and whistleblowers. Leaks often come slowly, allowing illegal activities to persist without exposure for years.

Just weeks after the attacks of Sept. 11, 2001, Bush approved the “warrantless wiretapping program,” which allowed the NSA to record phone calls and emails without court approval if one party was located outside the United States. Although the program violated surveillance laws and constitutional protections, the public did not learn about the illegal snooping until the New York Times, relying on leaks, reported on it four years later.

We may see leaks more promptly if the Trump administration perpetrates serious investigative abuses. At least, officials know by now that disclosure of such abuses will find a concerned audience and can have a major impact. The more that oversight from watchdog agencies, public advocates and Congress members is shut down, the more that journalists and privacy activists will seek out leaks and whistleblowers.

William Bendix is assistant professor of political science at Keene State College. Paul J. Quirk is professor and Phil Lind Chair in U.S. Politics at the University of British Columbia.