President Barack Obama has invited the entire Senate Democratic Conference to visit with him in the Eisenhower Executive Office Building on Tuesday evening.Sources said the expected topic of discussion is health care reform. Democratic Senate leaders have been scrambling to salvage the health care reform bill currently being debated as their moderates express more and more concerns with its scope.Sen. Joe Lieberman (ID-Conn.), an Independent who caucuses with Democrats, threw a wrench into Senate Majority Leader Harry Reid’s (D-Nev.) plans to pass a bill by Christmas when he threatened Sunday to filibuster the package over a proposal to expand Medicare. The tentative plan to allow those ages 55 to 64 to buy into Medicare was intended to assuage Lieberman and other Democratic centrists’ concerns over the bill’s public insurance option.Senate sources said the White House has urged Reid to try to cut a deal with Lieberman in order to secure passage by Dec. 25, but the White House disputed that Monday.