Now he has a new cause. Before the election, Mr. Feingold argued that whoever won should make a priority of rolling back Bush administration policies that eroded constitutional rights and disrupted the careful system of checks and balances. Now that Mr. Obama  a onetime constitutional law professor who made this issue a cause early in the campaign  has won the election, there is both reason for optimism and increased pressure on the president-elect to keep his promises.

Mr. Feingold has been compiling a list of areas for the next president to focus on, which he intends to present to Mr. Obama. It includes amending the Patriot Act, giving detainees greater legal protections and banning torture, cruelty and degrading treatment. He wants to amend the Foreign Intelligence Surveillance Act to restore limits on domestic spying. And he wants to roll back the Bush administration’s dedication to classifying government documents.

Many reforms could be implemented directly by the next president. Mr. Obama could renounce Mr. Bush’s extreme views of executive power, including the notion that in many areas, the president can act as he wants without restraint by Congress or the judiciary. Mr. Obama also could declare his intention not to use presidential signing statements as Mr. Bush did in record numbers to reject parts of bills signed into law.

Congress also has work to do. Many of the excesses of the last eight years have been the result of Mr. Feingold’s colleagues’ capitulation as much as presidential overreaching. He expects Congress to do more than just fix laws like the Patriot Act. He wants the Senate to question presidential nominees closely at their confirmation hearings about their commitment to the rule of law. And he hopes Congress will do its duty to impose the rigorous supervision it rarely imposed in the Bush years.

Restoring the rule of law will not be easy, Mr. Feingold concedes. Part of the problem is that it is hard to know how much damage has been done. Many programs, like domestic spying and extraordinary rendition  the secret transfer of detainees to foreign countries where they are harshly interrogated  have operated in the shadows.