Politicians learned long ago that one of the privileges of power is rigging the system to help your party and hurt the other. What they never seem to learn is how easily that trick can backfire. The shackles you fashion for your opponents can wind up on your own wrists.

Republicans learned that lesson back in the 1980s. After Franklin D. Roosevelt won four consecutive terms in the White House, they decided to make sure that could never happen again by pushing through a constitutional amendment saying that no one could be elected to the office more than twice. Revenge was sweet — until Ronald Reagan came along and some conservatives yearned for the chance to keep him in office beyond eight years.

Democrats, of course, rejected any notion of repealing the 22nd Amendment. They in turn lived to regret their approach — when Bill Clinton, the first Democrat since FDR to win a second term, was foreclosed from a third.

Illinois lawmakers had the chance to strip Rod Blagojevich of the power to appoint a replacement for Barack Obama in the U.S. Senate and give that power to voters. But they stalled and we all got burned by Blagojevich's appointment of Roland Burris.

Massachusetts Democrats are suffering their own self-inflicted wound. In 2004, when Sen. John Kerry was running for president, they wanted to block Republican Gov. Mitt Romney from choosing a successor if Kerry won. With control of the legislature, they passed a law taking away the governor's appointment power and requiring special elections to fill vacancies. It was political gamesmanship, though it also had the virtue of empowering the people to choose their own senator.

But today, many of those lawmakers are not content for virtue to be its own reward. The death of veteran Sen. Edward Kennedy opens up a vacancy, and this time the governor is Deval Patrick, a Democrat. So Patrick and some Democratic legislators want to restore his power to appoint a replacement to serve until the special election, which by law must take place from 145 to 165 days after the vacancy appears (Jan. 19 being the date chosen by Patrick). Kennedy himself endorsed the appointment idea in his final weeks.

The rationale of supporters is that they don't want the state to be without two senators for five months. But that prospect didn't bother them back in 2004. If Romney were still in office, Democratic lawmakers in Boston would be happy to leave the seat open until the voters could have their say.

Massachusetts Republican Party Chairwoman Jennifer Nassour had it right when she said, "If legislators go through with this, they are gigantic hypocrites." Even some of her usual foes seem to agree. Democratic state Sen. Brian Joyce, who supported the 2004 change, says authorizing an appointment by the governor "would be wholly undemocratic." The change might be politically unwise as well because it would taint Democrats running in the special election.

Come January, Massachusetts Democrats will have the chance to persuade voters to elect one of their own to Kennedy's seat. In the meantime, they may be reminded of what H.L. Mencken observed: "Injustice is relatively easy to bear; what stings is justice."