Sotomayor heads into what could be a couple weeks of testimony prior to a confirmation vote that Democrats are hoping to hold before the August recess. She is unlikely to testify on her own behalf until Tuesday as the 12 Democrats and seven Republicans offer their opening statements on the first day of the hearing.
Republicans have expressed concerns that the "wise Latina" will use her biases rather than constitutional precedence to interpret law.
"Certainly the rule of law depends on the same rules applying to each one of us, no matter our color, our sex or ethnicity," said Sen. John Cornyn, a former Texas Supreme Court judge.
Sen. Jeff Sessions, the top Republican on the Senate Judiciary Committee, told FOX News on Sunday that Sotomayor has repeatedly discussed in speeches over the last 10 years the influence of her personal experience on her decisions. He noted a 2001 speech in which the appellate court judge said she thought that a "wise Latina" often would reach better conclusions than a white male who couldn't have had the same life experience.
Sessions, himself denied by the Senate a seat on the federal bench more than 20 years ago, said the idea that a woman and a man can't reach the same conclusion is a philosophy that is incompatible with the American system.
"In the American system of justice, a judge takes an oath to be impartial and treat rich and poor alike," Sessions said. "She made a series of speeches that are troubling to me, flabbergasting, really, over a decade where she says a judge's personal feeling and background ... To me, that is unacceptable.
In his phone call Sunday, Obama told Sotomayor he was impressed with her diligence in talking to senators, said Press Secretary Robert Gibbs.
"He complimented the judge for making courtesy calls to 89 senators in which she discussed her adherence to the rule of law throughout her 17 years on the federal bench," Gibbs said. "The president expressed his confidence that Judge Sotomayor would be confirmed to serve as a justice on the Supreme Court for many years to come."
On Sunday, Sotomayor also received the endorsement of the International Association of Chiefs of Police. The White House pointed out that the IACP's backing amounts to Sotomayor's receiving the support of every major law enforcement organization in the U.S., representing nearly all of law enforcement.
Democrats say litigants before the high court have nothing to fear. Sotomayor's record shows her to be a "mainstream judge," Sen. Patrick Leahy, chairman of the Judiciary Committee, told CBS' "Face the Nation."
Sen. Chuck Schumer, D-N.Y., who will introduce Sotomayor to the panel on Monday, called her a meticulous judge who "goes out of her way, as a good jurist should, to follow the law, no matter what her sympathies tell her."
The "wise Latina" remark also creates a difficult proposition for Republicans who don't want to appear discriminatory in their opposition to a female, Hispanic judge. Cornyn, R-Texas, highlighted the potential political pitfalls for Republicans when he noted on "FOX News Sunday" that a third of his constituents are Hispanic.
"I understand that what they want, and what every nominee deserves, is for the nominee to be treated with respect. And we will. We're not going to filibuster Judge Sotomayor like the Democrats did Miguel Estrada, who would have been on the Supreme Court ... if he had not been filibustered and denied an up or down vote."
But racial bias forms the most notable area of dissent, as Sotomayor has also ruled against white firefighters in New Haven, Conn., who performed better on a promotion exam but were denied promotions.
The Supreme Court agreed in a 5-4 vote last month that the firefighters were wrongly denied their promotions, reversing a decision by Sotomayor and two other federal appeals court judges.
Republicans might use the wise Latina comment and the New Haven case "to imply that Sotomayor is a prisoner of identity politics," said David Garrow, a Cambridge University historian who follows the court.
"A lot of it is going to really depend not on particular answers but on how she comes across as a personality," Garrow said.
The subtext of the hearings has less to do with Sotomayor than with eventual other high court vacancies Obama might get to fill.
"A lot of it is about the future of the Supreme Court and future nominees," said Doug Kendall, president of the liberal Constitutional Accountability Center.
The GOP wants to "try to effectively state their vision for the Supreme Court and their concern with where President Obama's nominees could take the court," Kendall said.
Brian Fitzpatrick, a Vanderbilt University law professor who worked for Cornyn during the two most recent Supreme Court confirmation hearings, said, "Even if you can't defeat the nomination, perhaps you will get public opinion a little more behind the Republican party."
But even as identity politics and racial equality take the main stage, lurking in the background are two other issues that opponents say are troubling about the nominee. The perennial issues of abortion and gun rights are also going to have another airing during this week's testimony.
Already demonstrations have been held outside the Supreme Court building all weekend. A prayer vigil was also scheduled for Sunday night. Among the witnesses at the hearing is Charmaine Yoest, president of Americans United for Life. Yoest said Sotomayor's record shows her to be unabashedly pro-choice.
"She served as head of the litigation committee of a group called the Puerto Rican Legal Defense Fund that had a radical pro-abortion record opposing things like parental consent and bans on partial abortion. We need senators to understand that a vote for Sotomayor is a vote for unrestricted abortions on demand," Yoest said.
Also troublesome for critics are Sotomayor's claims that the Second Amendment doesn't apply to the states.
"This is a thunderous opinion. ... Her language is excessive in my view," Sessions said. "It's up in the air. The Supreme Court will rule on that in the next year or two. No doubt about it. It's a critically important case for those who believe in the right to keep and bear arms."