WASHINGTON - The Constitution does not say what criteria the Senate should use in deciding whether to confirm a Supreme Court nominee.
But at least one clear test has emerged over the first three days of Judge Samuel A. Alito Jr.'s confirmation hearings. This nominee must, it seems, continually refer to and, if at all possible, endorse the views of the woman he aims to replace, Justice Sandra Day O'Connor.
Senators from both parties have frequently used Justice O'Connor's opinions as a basis for questioning Judge Alito. The heavy emphasis on her work is a testament to her disproportionate influence on the court in her 25 years of service, and a reminder of the important role Judge Alito will assume if he is confirmed.
As two senators noted in their opening statements, Justice O'Connor has cast the decisive vote in almost 150 cases, many of them of great moment.
Whenever the opportunity arose, Judge Alito and his supporters highlighted instances in which he had ruled as she had. He invoked her name on 9 occasions, and he had good things to say about her decisions 10 times. On Tuesday, Senator John Cornyn, Republican of Texas, ticked off areas in which the two judges had agreed.
"Justice O'Connor and Judge Sam Alito both set limits on Congress's commerce power," Mr. Cornyn said. "Sandra Day O'Connor and Sam Alito both struck down affirmative action policies that had strict numerical quotas. And both - this ought to be a shocker to some based on what we've heard here today - is that both Justice Sandra Day O'Connor and Judge Sam Alito have criticized Roe v. Wade."
Democratic senators, on the other hand, worked hard to show that Judge Alito and Justice O'Connor were at odds, particularly in an important abortion case.
In his opening statement, striking a theme that has run through the hearings, Senator Charles E. Schumer, Democrat of New York, asked rhetorically, "Are you in Justice O'Connor's mold or, as the president has vowed, are you in the mold of Justices Scalia and Thomas?"
By Wednesday morning, Senator Tom Coburn, Republican of Oklahoma, had grown frustrated with all the O'Connor talk. "The fact that you have to fit the Sandra Day O'Connor mold is really a misapplication," he said. "There is no precedent that would say that."
Judge Alito said he would be his own person, but not before offering one more tribute. "No nominee can ever be a duplicate of someone who retires," he said, "and particularly when someone retires after such a distinguished career and such a historic career as Justice O'Connor. Nobody can be expected, as a nominee, to fit that mold."