U.S. Sen. Ben Nelson of Nebraska on Saturday threw his support behind the Democrats’ health care reform bill, giving the party the crucial backing it needed to avoid a Republican filibuster that would prevent a Senate vote.

The first of a series of votes is set for Monday at 1 a.m., on a so-called manager’s amendment, consisting of amendments crafted in the last week-and-a-half by Senate Majority Leader Harry Reid of Nevada.

At the request of Republicans, the entire package of amendments – 383 pages – was being read Saturday, for hours, on the Senate floor.

The Senate could vote on the entire bill, a top priority of President Obama, before December 25th.

Sen. Mitch McConnell, the Senate Republican leader, said the latest version of the Senate health care bill “is a legislative train wreck of historic proportions.”

“If [Democrats] were proud of this bill, they wouldn’t be doing it this way,” McConnell said. “They wouldn’t be jamming it through in the middle of the night on the last weekend before the holiday.”

McConnell said the legislation “will have a profound impact on our nation. This is not renaming a post office. Make no mistake, this bill will reshape our nation and our lives.”

Reid and Sen. Charles Schumer of New York spent most of Friday trying to answer concerns from Nelson, who had held back on supporting the bill because of his objections to public funding for abortions.

Schumer said negotiations with Nelson over the legislation’s health care provisions began Friday morning and ended with handshakes close to 11 p.m.

Schumer and others involved in the talks said Nelson didn’t want to make a public announcement about his decision to back the bill until the negotiated abortion language was entered into the record.

Nelson’s backing gave the Democrats the crucial 60 votes needed to move the bundle of recent amendments, which involved a spate of compromises, to the Senate floor.

“Change is never easy, but change is what’s necessary in America today. That’s why I intend to vote for cloture and for health care reform,” the Nebraska Democrat told reporters.

Cloture is the procedure that allows senators to place a time limit on consideration of a bill or other matters, and thereby overcome a filibuster.

Nelson warned, however, that if there are changes to the health bill when House and Senate leaders meet to resolve their differences, he will withdraw his support. The House has passed a different version of the bill.

(MORE at CNN.com)