"The truth is this issue is very complex. There is no easy fix and it's imperative that we build on what's already working in health care in America," Lincoln told her Senate colleagues.
Hours earlier, Landrieu had delivered her news. The two represent votes 59 and 60 for Senate Majority Leader Harry Reid, D-Nev., who needs that many in the 100-member Senate to go forward.
The Senate's 40 Republicans are unanimously opposed.
"I've decided that there are enough significant reforms and safeguards in this bill to move forward, but much more work needs to be done," Landrieu said, with the 8 p.m. EST vote looming.
Most everyone would be required to purchase insurance under Reid's legislation, and billions in new taxes would be levied on insurers and high-income Americans to help extend coverage to 30 million uninsured. Insurance companies would no longer be allowed to deny coverage to people with medical conditions or drop coverage when someone gets sick.
A largely overlooked provision in the Senate bill would send $100 million to Louisiana to help it cover costs for Medicaid, the federal-state health care program for the poor. In her speech, Landrieu rejected the notion that she was voting to advance the bill simply because of the money.
"I am not going to be defensive about asking for help in this situation," she said, recalling the devastation inflicted on her state by Hurricane Katrina in 2005 and her Republican governor's support for the provision. "I'm proud to have asked for it. I'm proud to have fought for it. And I will continue to."
During earlier debate on the bill, Democrats called a revamp of the nation's health care system long overdue.
"The country suffers when there is a failure to act on serious challenges that millions of ordinary Americans face in their daily lives," Sen. Patrick Leahy, D-Vt., said during the rare weekend session.
United in opposition, Republicans cast the bill as a costly government takeover, built on budget gimmicks.
"Move over, Bernie Madoff. Tip your hat to a trillion-dollar scam," said Sen. Kit Bond, R-Mo., referring to the mastermind of a multibillion-dollar Ponzi scheme.
The action in the Senate comes two weeks after the House approved a health overhaul bill of its own on a 220-215 vote. After the vote Saturday night, senators will leave for a Thanksgiving recess. Upon their return, assuming Democrats prevail on the vote, they will launch into weeks or more of unpredictable debate on the health care bill, with numerous amendments expected from both sides of the aisle and more 60-vote hurdles along the way.
Senate leaders hope to pass their bill by the end of the year. If that happens, January would bring work to reconcile the House and Senate versions before a final package could land on Obama's desk.
The bills have many similarities, including the new requirements on insurers and the creation of new purchasing marketplaces called exchanges where self-employed individuals and small businesses could go to shop for and compare coverage plans. One option in the exchanges would be a new government-offered plan, something that's opposed by private insurers and business groups.
Differences include requirements for employers. The House bill would require medium and large businesses to cover their employees, while the Senate bill would not require them to offer coverage but would make them pay a fee if the government ends up subsidizing employees' coverage.
Another difference is in how they're paid for. The Senate bill includes a tax on high-value insurance policies that's not part of the House bill, while the House would levy a new income tax on upper-income Americans that's not in the Senate measure. The Senate measure also raises the Medicare payroll tax on income above $200,000 annually for individuals and $250,000 for couples. Both bills rely on more than $400 billion in cuts to Medicare.