Health care legislation squeaked out of committees and passed the House on party-line votes, plus or minus a few "mavericks" or Blue Dogs here and there. So don’t expect that the upcoming debate in the Senate will burst into bipartisanship. Majority Leader Harry Reid faces the prospect of defections from the Democratic caucus and will need to woo moderate Republicans if the bill is to preserve the mantle of bipartisanship. After all, Speaker Nancy Pelosi wrangled Republican Rep. Joseph Cao of Louisiana to vote in favor.

These are the six senators most likely to cross party lines in the health care debate and who could become pivotal in shaping the reform with amendments even if they don’t vote for the final product.

Sen. Ben Nelson, D-Neb.

A strong conservative voice in the Democratic Party, Nelson is an advocate for strong anti-abortion language along the lines of the Stupak-Pitts amendment in the House and is reportedly unhappy with the abortion provisions in Reid’s bill. He also opposes the public option in its current form but has said he would be amenable to a trigger.

The senator often responsible for pulling Democratic bills to the right is trying once again to moderate the bill so it might appeal to some Republicans. In September, he said the bill would only be legitimate if it passed with 65 votes. He has not blocked the bill’s progress so far, instead voting it onto the floor, where moderates on both sides may be able to hash out acceptable details. Ahead of the cloture vote, Nelson described debate as "an opportunity to make improvements." And he wondered to no one in particular: "If you don't like a bill, why block your own opportunity to amend it?"