Few pardons have had a more lasting effect than President Clinton’s 11th-hour decision to forgive Marc Rich, a wealthy financier who fled the United States shortly before being charged with multiple counts of fraud, racketeering and tax evasion.

Senior Bush and Obama administration officials acknowledged that the furor over the Rich pardon changed the political landscape, making presidents much more cautious about using a Ccnstitutional power that is without limit.

Judge Abner Mikva, who served as one of Clinton's White House counsels and was a mentor to Obama, said the president had confided a deep concern about the Rich affair.

"I think Marc Rich looms larger with Barack Obama than with other presidents because I think he was very, very dismayed by the Marc Rich pardon and the basis on which it appears to have been granted," Mikva said. "To him and to most people, it was the epitome of what could go wrong."

Rich, a commodities-trading billionaire, received his pardon after his ex-wife, Denise, made substantial donations to the Democratic Party and the Clinton Presidential Library. The perception that Clinton had sold a presidential pardon touched a nerve with the public and Congress, which held months of emotional hearings.

Eric Holder, the departing deputy attorney general and current attorney general, expressed emotional regret for his role, which included encouraging Rich’s attorneys to directly approach the White House. Democrats concentrated their fire on the lawyer who pressed prosecutors to withdraw Rich's indictment: Scooter Libby, the incoming chief of staff for Vice President Dick Cheney.

The president's authority to grant pardons is enshrined in the Constitution and cannot be undone by any other branch of government. Presidents can pardon anyone, from individuals to large groups, and can act at any moment in a federal criminal case. Another historic act of clemency — President Gerald Ford's pardon of Richard Nixon — occurred before any charges had been brought.

In the aftermath of the Rich case, President George W. Bush decided to rely more on recommendations from the career officials in the Justice Department's Office of the Pardon Attorney. Bush hoped that this would discourage the politically well-connected from directly lobbying the White House.

"There were two lessons," said Alberto Gonzales, who served as Bush's White House counsel and then attorney general. "There are political consequences to grants and political consequences when you go against the recommendation of the Department of Justice."

Kenneth Lee, who served as associate White House counsel during Bush's second term, said Rich was always on the minds of those vetting pardon applicants. "You can't overestimate the shadow of that case. There is very little political benefit in granting pardons or commutations, but the blowback can be huge. We probably would have recommended a lot more pardons to the president, but we were reluctant to do so if DOJ didn't recommend them."

Officials acknowledge that Bush accepted the recommendations of the pardon office in almost every case, even as he grew frustrated with the small number of potential pardons forwarded to him.

Bush granted the fewest pardons — 189 — of any modern-day president except his father, who served only one term. Obama is on pace to be even more parsimonious, forgiving only 22 people in his first three years in office while rejecting nearly 900. Officials said he has continued Bush's practice of following the pardon office's recommendations.

The 2001 hearings on the Rich pardon lasted for months. When the testimony was over, the politics of pardons were fundamentally changed. Mark Corallo, formerly the Republican communications director of the House Committee on Oversight and Government Reform, said that in a moment of “bad judgment’’ Clinton had “damaged the ability of future presidents to pardon."

"The one thing we did learn is that pardons are wonderful,'' Corallo said. "We got to look at cases of people who had been pardoned and thought, ‘Wow, this is justice done when the president grants a worthwhile pardon.' Our justice system is supposed to be tempered with mercy, and to pardon someone deserving is an incredibly wonderful thing."