Already weary from the months of negotiating in committees and from the relentless lobbying of interest groups and of the White House, Senators will virtually be locked inside their chamber for as long as it takes to reach a final vote on a reform bill drafted by George Mitchell, the leader of the Democratic majority.
A parallel endeavour will begin in the House of Representatives on the other side of the Hill on Monday. For all members of Congress, the healthcare marathon means that the August recess, which normally would have begun at the end of this week, will certainly be delayed if not lost altogether.
The goal is for both houses to approve their own versions of healthcare reform before any holiday is taken. Neither side is expected to vote for at least two weeks. When business resumes next month work would begin in a Senate-House conference to reconcile the two texts and draft a final, unified bill. Voting on that version would probably occur in October.
While everyone is agreed on the historic importance of the issue - both politically for President Bill Clinton and economically for the country as a whole - nobody is sure what the next weeks will bring.
There remains a significant chance that ideological divisions on both side of the Hill will prove insurmountable and cause the entire effort to founder.
Failure would be calamitous for the President, who is betting on healthcare reform to resuscitate his fortunes. The White House was yesterday preparing an all-out campaign to hammer home to the public and wavering congressmen its message that it is now or never for serious reform.
'I think you can expect to see a full administration blitz over the next couple of weeks as we work to get these bills through the House and Senate', Dee Dee Myers, the White House spokeswoman, commented yesterday.
The Mitchell bill, all 1,410 pages of it, sets out to guarantee insurance coverage for 95 per cent of Americans by the turn of century, mostly by subsidising health insurance costs for the poor. A commission would then be convened to discuss extending coverage to the remaining 5 per cent by 2002.
While President Clinton has indicated he could accept the Mitchell version, it is a pale shadow of the overhaul that was originally tabled by the White House and composed in part by Hillary Rodham Clinton. The bill before the House of Representatives, presented by Richard Gephardt, the majority leader, is more ambitious and seeks full insurance for all Americans by 1999.
Most contentious is the issue of how universal coverage should be funded. Both the original White House model and the Gephardt text would require employers to pay 80 per cent of the insurance premiums of workers.
It is this requirement that stirs most opposition from Republicans and conservative Democrats. The Mitchell bill attempts a tricky middle road on the question. At first no contribution obligation would be imposed on employers. If, however, the aim of coverage for 95 per cent of Americans is not achieved by the turn of the century, an employer mandate would be triggered under which companies would be responsible for 50 per cent of their workers' coverage costs.
Republicans are unimpressed with the compromise. Most ominous, as the debate gets underway, have been threats from leading Republicans to stage a filibuster to block final votes. Senator Phil Gramm, of Texas, warned: 'Anything I can do within the rules of the Senate to prevent the government from taking over or controlling the health care market, I'm going to do.'