All eyes are on Republican Sens. Bob Corker (Tenn.) and Arlen Specter (Pa.) as potential vote-switchers on the Medicare doctor’s fix.

Republican sources also said they were watching Sens. Mel Martinez (R-Fla.) and Kay Bailey Hutchison (R-Texas).

Democrats need just one vote to achieve cloture on the bill and Republicans are being heavily pressured by the White House not to cave to their demands. The vote is slated for 4 p.m. today.

“I’ve got concerns about the way both sides have handled this. This is about what is the right policy position to take,” Corker said.

Corker predicted that if he supported cloture that there would be an “avalanche” of other Republicans to accompany him.

“I’m just not going to comment right now,” Hutchison said.

Vice President Cheney was at the Republican Senate luncheon on Wednesday and although no one would detail his pitch, Sen. Jon Kyl (R-Ariz.) conceded that the White House plans to veto the Medicare bill.