WASHINGTON -- The Senate is starting a historic debate on Supreme Court nominee Sonia Sotomayor, who's on track to be confirmed this week to be the first Hispanic and third female justice.

Republicans have lined up almost solidly against President Barack Obama's nominee, taking what strategists in both parties call a steep political risk in opposing Sotomayor, although a handful of GOP senators are siding with Democrats to support her.

Sotomayor, 55, is the daughter of Puerto Rican parents who was raised in a South Bronx housing project and educated in the Ivy League before going on to success in the legal profession and 17 years on the federal bench. Obama chose her to replace retiring Justice David Souter, a liberal named by a Republican president, and she's not expected to alter the court's ideological balance.

Still, Republicans call her an activist who would bring bias to the bench, pointing to a few rulings in which they argue she showed disregard for gun rights, property rights and job discrimination claims by white employees. They're also unsatisfied with Sotomayor's explanation of a 2001 speech -- similar to comments she's made throughout her career -- in which she said she hoped a "wise Latina" would usually make better decisions than a white male.

Democrats point instead to a long record of rulings in which Sotomayor has reached the same conclusions as judges who are considered more conservative. They call her a moderate who is restrained in her legal interpretations and argue that her controversial remarks -- while perhaps worded inartfully -- show nothing more than a belief that diverse experiences help a judge see all sides of a case.

Some in the GOP have faced a tough call about how to vote on Obama's nominee, torn between an impulse to please their conservative base by opposing her and a fear that doing so could alienate Hispanic voters. The vast majority are lining up with their core supporters against Sotomayor, despite her near certainty of being confirmed.

The decision was further complicated for some senators in both parties after the National Rifle Association announced it would downgrade senators who supported Sotomayor in its annual candidate ratings. Still, many Democrats and a couple of Republicans with perfect or near-perfect scores from the group are defying the NRA and voting for her anyway.