Everyone recalls “Mr. Smith Goes to Washington,” but too few remember the real-life Mrs. Smith. So, as the Senate nears a vote on a proposal to unilaterally change Senate rules for confirming federal judges, I am reminded of the words spoken 55 years ago by Sen. Margaret Chase Smith of Maine in her famous “Declaration of Conscience” against the tactics of Sen. Joe McCarthy, a member of her own party.

“I don’t believe the American people will uphold any political party that puts political exploitation above national interest,” the senator said. “Surely we Republicans aren’t that desperate for victory. While it might be a fleeting victory for the Republican Party, it would be a more lasting defeat for the American people. Surely it would ultimately be suicide for the Republican Party and the two-party system that has protected our American liberties from the dictatorship of a one-party system.”

The circumstances are obviously different; there is no McCarthyism in the current dispute. But the principles of exercising independent judgment and preserving our system of checks and balances are at the heart of the Senate rules debate.

Sen. Smith embodied independence and understood the Senate’s singular place in our system of checks and balances. Our founders created that system to prevent abuse of power and to protect our rights and freedoms. The president’s veto power is a check on Congress. The Senate’s power to confirm or reject judicial nominees balances the president’s authority to nominate them. The proposal by some Republican senators to change rules that have governed the Senate for two centuries now puts that system in danger.

Since 1789, the Senate has rejected nearly 20 percent of all nominees to the Supreme Court, many without an up-or-down vote.

In 1968 Republican senators used a filibuster to block voting on President Lyndon B. Johnson’s nominee for chief justice of the Supreme Court. During the debate, a Republican senator, Robert Griffin, said: “It is important to realize that it has not been unusual for the Senate to indicate its lack of approval for a nomination by just making sure that it never came to a vote on the merits. As I said, 21 nominations to the court have failed to win Senate approval. But only nine of that number were rejected on a direct, up-and-down vote.”

Between 1968 and 2001, both parties used filibusters to oppose judicial nominees. In 2000, the last year of Bill Clinton’s presidency, Republican senators filibustered two of his nominees to be circuit judges. They also prevented Senate votes on more than 60 of Mr. Clinton’s judicial nominees by other means.

So much for the assertion that filibustering to prevent votes on judicial nominees is a new tactic invented by Senate Democrats.

Senate rules can be changed, and they often have been. But Senate Republicans don’t have the votes for a change within the rules. So they propose to go around them, to act unilaterally to get their way. It’s what they call the “nuclear option.”

They claim that their actions are justified because the filibuster is being used unfairly to stop the confirmation of President Bush’s nominees. But 208 of the president’s 218 judicial nominees have been approved. That’s right: the Senate has confirmed 95 percent of Mr. Bush’s judicial nominees. That’s a higher percentage of approval than any of his three predecessors achieved.

During my six years as majority leader of the Senate, Republicans, then in the minority, often used filibusters to achieve their goals. I didn’t like the results, but I accepted them because Republicans were acting within the rules; and we were able to work together on many other issues. There were 55 Democratic senators then. We had the power to take the drastic action now being proposed, but we refrained from exercising that power because it was as wrong then as it is now.

Most Americans may not be aware of the complexities of the Senate’s rules, but they do know and understand two fundamental principles: playing by the rules and dealing fairly with others.

The nuclear option violates both. If it’s exercised, I hope that enough modern-day Sen. Smiths, guided by what is best for the nation and the Senate, will vote to stop it.

George J. Mitchell is a former majority leader of the Senate.