The Moderate Republicans
In the dwindling ranks of G.O.P. centrists who might oppose conviction, JOHN CHAFEE of Rhode Island, and JIM JEFFORDS of Vermont, have been crossover allies of the President. Jeffords supported health-care reform, and Chafee is an environmentalist. Both are eyed with suspicion by conservatives, who want them stripped of their committee chairmanships. Maine's freshman Senators, SUSAN COLLINS and OLYMPIA SNOWE, are also outcasts; both are pro-choice. Their views of the case against Clinton will be critical.

The Free-Spirit Democrats -- Bearers of Bad News
The four Democrats to watch for signs of trouble for Clinton are ROBERT BYRD of West Virginia, who opposes attempts to bypass a trial as unconstitutional; JOE LIEBERMAN of Connecticut, who rebuked the President in September; PAT MOYNIHAN of New York, who is always immune to partisan entreaties; BOB KERREY of Nebraska, who once called Clinton "an unusually good liar." If Democrats decide Clinton should resign, the job of telling him will fall to such allies as minority leader TOM DASCHLE of South Dakota; Hillary pal JAY ROCKEFELLER of West Virginia; and TED KENNEDY of Massachusetts.

Clinton Foes / Clinton Defenders
If the Senate trial degenerates into a partisan brawl, the White House will rely on two former House Democrats to fight for the President. New Jersey's ROBERT TORRICELLI, who partly owes his Senate victory in 1996 to the President, will prove his loyalty--and his desire to be Al Gore's Vice President. New York's CHARLES SCHUMER, defended Clinton in the House Judiciary Committee and will reprise that role when he moves to the Senate in January. He and Torricelli will clash with the G.O.P.'s anti-Clinton caucus, led by RICK SANTORUM of Pennsylvania, and DON NICKLES of Oklahoma. A favorite of the Christian right, Nickles will watch Trent Lott for signs of premature compromise. Nickles and Santorum represent the younger, more ideological breed of Senate Republican.

The Mysterious Incoming Senators
New faces will include Democrats JOHN EDWARDS of North Carolina and EVAN BAYH of Indiana, moderates with a tenuous allegiance to Clinton. Ohio's GEORGE VOINOVICH is a moderate too, but Republican.