WASHINGTON — After incurring their wrath for his handling of the investigation into Hillary Clinton’s email use, some Democrats now see James B. Comey, the F.B.I. director, as a potential ally in trying to block President-elect Donald J. Trump’s promises to revive the practice of sending terrorism suspects to the military prison at Guantánamo Bay, Cuba, and interrogate them using banned techniques such as waterboarding.
For three years, Mr. Comey has helped carry out President Obama’s counterterrorism vision, in which F.B.I. agents have interrogated suspected terrorists and turned them over to the Justice Department for prosecution in criminal courts. During his confirmation hearing in 2013, Mr. Comey told the Senate Judiciary Committee that he believed waterboarding was torture.
Mr. Trump’s nominee to serve as attorney general, Senator Jeff Sessions, has been a fierce critic of the Obama administration’s approach. He has argued that terrorism suspects should be sent to Guantánamo Bay and interrogated without access to lawyers and the right to remain silent. If confirmed, Mr. Sessions would be Mr. Comey’s boss.
Mr. Sessions has also said the United States weakened itself by banning techniques such as waterboarding, which he said were legal and effective. He voted against the Detainee Treatment Act in 2005 that prohibited cruel or degrading treatment of detainees. Last year, he voted against legislation requiring all government agencies to use only interrogation methods in the Army Field Manual. Those techniques do not include waterboarding.
Mr. Sessions has said he would not rule out waterboarding again. “This would be unwise advice to the enemy we face,” the senator said in 2008. He has opposed the closing of the Guantánamo Bay prison and the transporting of terrorists to the United States to face trial in federal court.
The positions taken by Mr. Comey in recent years could put him at odds with not just Mr. Sessions but other members of Mr. Trump’s national security team.
“Given the recent slate of appointments from the president-elect, F.B.I. Director Comey may well turn out to be a bulwark against the worst abuses and provide some defense of the rule of law,” said Faiza Patel of the Brennan Center for Justice at New York University, who is a frequent critic of the F.B.I.
Lt. Gen. Michael T. Flynn, who was offered the key position of national security adviser in the Trump White House, has said he might be open to using enhanced interrogation techniques, with certain limits, if the country faced a terrorism attack using weapons of mass destruction or another grave threat.
Representative Mike Pompeo, Republican of Kansas, Mr. Trump’s choice to run the Central Intelligence Agency, is an advocate of restarting the agency’s detention and interrogation program, which Mr. Obama ended.
Mr. Pompeo has criticized Mr. Obama’s decision in January 2009 to shut down the agency’s black-site prisons and require all interrogators to strictly adhere to anti-torture laws and use only Army Field Manual interrogation techniques. In 2014, he accused Mr. Obama of refusing “to take the war on radical Islamic terrorism seriously,” citing among other policies the “ending our interrogation program in 2009.”
Mr. Pompeo also took aim at a Senate report on the C.I.A. detention and interrogation program, saying its release had put American lives at risk.
Under Mr. Comey, the F.B.I. has worked with the military to capture and prosecute high-profile terrorism suspects in federal court. In 2014, F.B.I. agents and Army Delta Force commandoes captured Ahmed Abu Khattala, a suspected ringleader of the 2012 terrorist attacks in Benghazi, Libya, and took him to a Navy ship in the Mediterranean Sea. Republicans, including Mr. Pompeo, criticized the administration, saying Mr. Khattala should have been taken to Guantánamo Bay.
Daniel Jones, a former F.B.I. analyst who led the Senate investigation into the C.I.A. detention and interrogation program, said there was no guarantee that Mr. Comey would ally himself with Democrats to oppose a change in policy under Mr. Trump. Mr. Comey’s refusal while deputy attorney general in the George W. Bush administration to sign on to a National Security Agency surveillance program — an action that burnished a reputation for political independence — “doesn’t mean he’s not a conservative Republican in opposition to the Democratic agenda,” Mr. Jones said.
Mr. Comey drew criticism from Democrats after notifying Congress on Oct. 28 that the F.B.I. had discovered emails potentially relevant to the case involving Mrs. Clinton’s use of a private email server as secretary of state, only to say days before the election that they did not change his determination that she should not face charges. Mrs. Clinton, among others, has said his actions contributed to her losing the election.
Ali Soufan, a security consultant and former F.B.I. agent who has supported criminal trials for terrorists, said Mr. Comey deserved credit for making hard decisions in the email case. He predicted Mr. Comey would do the same in a new administration. “Will he win all the arguments? I don’t believe so,” he said. “Will he stand up and fight? I believe so.”