Hatch, 75, has been the committee chairman twice and participated in hearings for eight Supreme Court justices. A musician and great-grandfather, Hatch is known for a generally cool demeanor that sometimes gives way to frank rejoinders.

He has a strong conservative philosophy, and in past hearings he staunchly defended the troubled nominations of Robert Bork (who wasn't confirmed) and Clarence Thomas (who was). But Hatch has departed from party dogma, too, on stem cell research and other issues.

He has said he's concerned that Sotomayor takes a "somewhat dim view of the Second Amendment" to the Constitution to keep and bear arms. But he also has said he's keeping an open mind and generally believes presidents should be given leeway on the people they nominate.

THE WILD CARD

Sen. Arlen Specter, D-Pa.

"Snarlin' Arlen," 79, enters these hearings more experienced at running them than Leahy, yet without the privileges of the seniority that ordinarily comes with five Senate terms.

Democrats stripped him of that when he joined their party this year. He switched, he said, because he could not have won a GOP primary in Pennsylvania as a Republican.

Specter is not expected to behave in the traditionally deferential manner of a junior senator. He was chairman at the hearings of now-Chief Justice John Roberts and Justice Samuel Alito. And he knows Senate tradition, the law and the Constitution as well as any expert in the room. He's famous for bucking the leadership of his party, a trait that vexed the Bush White House.

THE DOYENNE

Sen. Dianne Feinstein, D-Calif.

In her fourth term, Feinstein, 76, is the most senior woman on the committee and represents a statewide constituency that is 36 percent Hispanic and half women, according to the Census Bureau.

Feinstein told reporters last week she plans pushing back hard against any Republican implication that Sotomayor might be an "activist judge" who tries to make laws from the bench. Roberts and Alito, Feinstein said, have participated in high court reversals of precedent plenty of times since their confirmations, though they pledged to not be activists.

Now head of the Senate Intelligence Committee, Feinstein has considerable clout in the Senate and with Obama's White House. Viewers might recall her presiding over Obama's inauguration in January.

THE SKEPTIC

Sen. John Cornyn, R-Texas.

The second-term senator, 57, has perhaps the best picture of this particular nomination and its political implications of anyone on the panel. Like Feinstein, he represents a large state and a constituency that's about one-third Hispanic.