The battle over health care now heads to the Senate.

With the historic passage of a massive health care overhaul (HR 3962 ) in the House, the fate of the legislation will now be decided in the Senate.

Over the weekend, President Barack Obama urged the Senate to finish work on the bill by the end of the year and "bring this effort to the finish line."

Senate Majority Leader Harry Reid is waiting to hear back from the Congressional Budget Office on the estimated costs of a combined bill, according to CQ reporters Drew Armstrong and Alan Ota.

Several issues are in play:

* Filibuster. Sen. Joe Lieberman (ID-Conn.) and some Republican senators have threatened to filibuster the bill, forcing Reid to get 60 votes to get the bill across the finish line.

* Public option. Conservatives oppose any kind of government-run plan in the plan. Reid may push an "opt-out" or "trigger" provision to allow states not to participate to win over moderates.

* Cost. The House version of the bill cost $1.1 trillion. Conservative senators of both parties may be skeptical if the CBO's score of the Senate version is too high.

* Abortion. In a last-minute compromise, the House added restrictions on abortion coverage in new insurance programs created by the bill. The Senate bill will likely not be as restrictive.

* Illegal immigrants. Members of the Congressional Hispanic Caucus have threatened to oppose the bill if it includes any tougher language prohibiting illegal immigrants from buying insurance.

In addition, Reid is running for re-election in his home state of Nevada in 2010, complicating his duties as Democratic leader.

Ryan Teague Beckwith is deputy editor of Congress.org.