Watch how Maine Republican Olympia Snowe and Arkansas Democrat Blanche Lincoln vote in the Senate Finance Committee on the Baucus version of the Obama health care plan. As Snowe and Lincoln go, so will the Congress.

The Democrats need Snowe's vote desperately to convince wavering moderate Democrats that they can offer a veneer, however thin, of bipartisanship to the health proposal. If Snowe, their last chance at a Republican vote, opposes the Obama/Baucus proposal, there is no hope of a bipartisan fig leaf for the package.

On the other hand, if Snowe backs the bill, it will send a signal to moderate Democrats that it's OK to join in, and the bill will probably attract the 60 votes it needs for Senate passage.

Lincoln's vote becomes critical if Snowe votes "no." Lincoln of Arkansas is probably the single most vulnerable Democrat running for re-election in 2010. She is the proverbial canary in the coalmine. If she makes it, so will all the Democrats. Hailing from a conservative Southern state, her poll numbers suggest that she would be in a heap of trouble with a stiff challenger.

If Lincoln defects and joins the Republicans in voting "no" (as she has done on a number of amendments), she will do a lot to cement her chances to remain a senator, but will open a wound in the Democratic Party. A domino effect will likely set in. Her Arkansas colleague, Democrat Mark Pryor, will feel exposed by her defection and will probably consider voting no, as well. It will be very hard for the son of moderate David Pryor to explain why Lincoln jumped ship but he chose to stay on board.

Sen. Ben Nelson of Nebraska, encouraged by Lincoln's vote, will probably vote no, as well. These negative votes will bring huge pressure on Mary Landrieu, the Louisiana Democrat. Nor can the president count on the support of independent Joe Lieberman of Connecticut, who has warned that, despite his basic support for the concept of the bill, it would be hard for him to back it in the current economic and fiscal crisis.

Once Obama's plan will clearly fail to attract 60 votes, Majority Leader Harry Reid will fall back on reconciliation as a strategy and hope for 50 votes. But if the Democrats pass the bill with 50 votes, it will set a precedent they may come to rue. It would basically eliminate the filibuster as a parliamentary tactic and would condemn any future minority party (Democrats in 2011?) to the same irrelevance as afflicts their House colleagues. To be in the minority in a chamber run by a bare majority is not a fun task.

If Lincoln votes "yes," however, it will send a signal to all moderates that even the most endangered of their species is willing to risk backing the program and will do a great deal to shore up the president's defenses.

All this means that if the elderly citizens of Arkansas and Maine -- and their families -- want to avoid the evisceration of the Medicare program contemplated in the Baucus/Obama bill, they had better get busy. They need to deluge both senators with urgent pleas to vote against the $500 billion cut in the Medicare program. Neither senator can afford to alienate her elderly constituents, but what do they expect when they vote to take the hatchet to Medicare?

Newt Gingrich found out that cutting Medicare is a ticket to political oblivion. Barack Obama will learn the same lesson. The question is: Will Olympia Snowe and Blanche Lincoln join him?