After weeks of hand-wringing, Congress' top Democratic leaders have finally offered their own versions of health-care legislation for the consideration of their respective chambers and the American public.

Well, almost. Senate Majority Leader Harry Reid has not fully released his bill because he's waiting for the nonpartisan Congressional Budget Office to analyze its fiscal impact. President Obama has said he will sign only legislation that costs less than $900 billion and is deficit-neutral, so Reid and House Speaker Nancy Pelosi have their marching orders.

The lawmakers and their legislation face difficult choices, competing interests, growing pressure, and major hurdles ahead.

Two thorny political issues in particular threaten to derail the health legislation: abortion and immigration.

A group of 40 antiabortion Democrats is threatening to block the House legislation unless it includes stronger language prohibiting government funding for abortions.

On the immigration issue, Rep. Joe Wilson - whose "You lie!" outburst made him famous - is pushing to block illegal immigrants from receiving benefits. He argued that, while the legislation may say aliens cannot receive benefits, it lacked an enforcement provision. His point was validated when both the White House and the Senate Finance Committee agreed to the enforcement language he sought. If the final legislation does not meet Wilson's satisfaction, expect a revolt.

The prospects for passing health-care reform remain unclear for other reasons. Pelosi's 1,990-page bill includes a controversial public option and was scored by the CBO at a net cost of $894 billion, just under Obama's threshold. But the cost may rise, and questions about the bill's long-term impact on the deficit remain.

All of the House's Republicans are expected to vote against the bill, with the exception of vulnerable freshman Rep. Joseph Cao, who represents an overwhelmingly Democratic New Orleans district. To reach a simple majority, Pelosi will need 13 of 52 moderate Democrats - the so-called Blue Dogs - when she brings the bill to the House floor, perhaps as soon as Thursday.

Meanwhile, Reid's decision to include a public option in the bill threatens the fragile compromise that won the vote of one Republican senator, Maine's Olympia Snowe. The public option in the bill is said to include a provision for states to opt out, but Reid has not fully explained how it would work, and Republicans remain skeptical. One concern is whether states opting out would nevertheless be sending their tax dollars to Washington to fund the program for participating states.

Reid's decision to attempt to appease his liberal base has also imperiled the bill's ability to reach the important 60-vote threshold. Reid needs 60 votes just to bring up the bill, and he would need 60 votes again to end debate and allow a final vote, a procedure known as cloture. Actually passing the bill once debate ends would require only a simple majority of 51 senators.

The upshot is that Reid needs all 60 Democrats to vote with him - twice. (He could reduce the threshold to 51 votes with a procedural maneuver, but it's problematic.)

Led by Sen. Mitch McConnell (R., Ky.), Republicans have argued preemptively - and correctly - that a vote for cloture is a vote for the bill. That's meant to head off those Democrats who might take a tortured, John Kerry-esque stance by voting for cloture but against final passage.

A number of moderate Democratic senators have expressed at best tepid support and at worst serious reservations about Reid's bill. Independent Sen. Joe Lieberman of Connecticut has said he would join a Republican filibuster to block it. Budget hawk Kent Conrad (D., N.D.) will want to see how the bill affects the long-term deficit picture. Blanche Lincoln (D., Ark.), who is vulnerable and facing a reelection bid, has voiced concerns about a public option. And other moderates - from Florida, Nebraska, Louisiana, Montana, and Indiana - have yet to publicly support the bill and appear to be wavering.

In the end, politics is about reelection more than it is about anything else. As such, many Senate Democrats will vote the way they need to vote to protect themselves.

After months of debate, town-hall meetings, interviews, and cable-TV chatter, Democrats are closer to passing a bill. But they still have a long way to go.

Matt Mackowiak is the president of Potomac Strategy Group and has been a press secretary for two Republican senators.

He can be contacted at matt@potomacstrategygroup.com