... Lieberman has fought Democrats with the pluck of a third-grader in a dodge-ball tournament, advancing the view of him as a rogue ready to bolt the Democrats, where he caucuses, for the Republicans. And in a Politico interview last week, he once again refused to rule out the possibility.

Homeland Security and Governmental Affairs Chairman Lieberman is making it clear he does not want Iraq-related amendments attached to a bill scheduled for floor action this week that would implement unfulfilled recommendations of the 9/11 Commission. Democratic leaders seemed inclined today to hold off introducing Iraq-related amendments to the bill, possibly to avoid upsetting Lieberman and moving him closer to switching party affiliations, which would swing the Senate back to GOP control.

One Democratic aide quoted by CongressDaily says it “depends on whether Republicans push to attach language supportive of President Bush’s so-called surge in U.S. troop strength in the most dangerous areas of Iraq. ‘The Democrats won’t [offer Iraq amendments] if Republicans don’t,‘ this aide said.” Aides to Senate Majority Leader Harry Reid (D-NV) and Armed Services Chairman Carl Levin (D-MI) say they have not decided how to proceed with the Iraq proposals.

Lieberman says leaving the Democratic Party is a "very remote possibility." But even that slight ambiguity -- and all his cross-aisle flirtation -- has proved more than enough to position Lieberman as the Senate's one-man tipping point. If he were to jump ship, the ensuing shift of power to Republicans would scramble the politics of the war in Iraq, undercut the Democrats' national agenda and potentially weaken their hopes for the White House in 2008. Those stakes are high enough to give Lieberman leverage with both parties no matter how slim the chance of his crossing the aisle. Which means Senate leaders aren't worrying only about whether Joe Lieberman will switch parties. They're wondering what, if anything, he plans to do with the power that comes from keeping that possibility alive

Republican leaders decided not to seek special language spelling out the terms of a transition in case of a power shift -- say, if Johnson vacates his post and his state's GOP governor appoints a Republican to replace him. Under that scenario, power would effectively shift to Republicans, because Cheney would provide the tiebreaking 51st vote. But for Republicans to take parliamentary control, the Senate would have to vote for new organizational rules, a move Democrats could filibuster.

A similar scenario unfolded in January 2001, when a 50-50 Senate convened. In 2001, Democrats demanded a "kick-out clause" in organizing negotiations that would automatically scrap agreements on committee ratios and funding levels and force new organizational rules. But Republicans decided this month against a confrontation that would come from demanding a similar clause.

"Nobody over here talked about that at all," said Don Stewart, spokesman for McConnell.