U.S. President Barack Obama exhorted House Democrats on Saturday to stay true to their party's legacy and make history by bringing health insurance to millions of struggling families now left out.

Leaders exuded confidence as they defused thorny problems in the countdown to a landmark vote on Sunday.

Obama evoked Abraham Lincoln's moral compass and extolled Democratic achievements such as Social Security and Medicare — once controversial, now an essential part of the social fabric — on a day marked by a frenetic hunt for votes inside the Capitol and angry Tea Party demonstrations at the door.

Some protesters hurled racial insults at black members of Congress.

"Is this the single most important step that we have taken on health care since Medicare?" Obama asked rank-and-file Democrats far from the chanting crowds.

"Absolutely. Is this the most important piece of domestic legislation, in terms of giving a break to hard working, middle-class families out there since Medicare? Absolutely.

"It is in your hands," Obama said, bringing lawmakers to their feet. "It is time to pass health-care reform for America and I am confident that you are going to do it tomorrow."

Last-minute flare-ups

In a carefully orchestrated appeal to unity ahead of a career-defining vote, Obama and House leaders were joined by Senate Majority Leader Harry Reid, D-Nev., who brought a pledge from more than 50 of his Democratic colleagues to promptly finish the bill after the House votes Sunday.

House Democrats have been wary of being left in the lurch by the famously unpredictable Senate. A series of last-minute flare-ups threatened to slow the Democrats' march to passage, after more than a year of gruelling effort.

The most intense focus was on a small group of Democrats concerned that abortion funding restrictions in the legislation don't go far enough. Determined to avoid votes on such a charged issue, Democratic leaders raised the possibility of addressing the concerns of abortion foes through an executive order from Obama.

It would reaffirm existing federal law barring taxpayer-funded abortions except in cases of rape, incest or to save the life of the mother.

House Democratic leaders abandoned a much-challenged procedure for passing the legislation after an outcry from Republicans and protest from some of their members.

According to the new plan, the House will vote up or down the health-care bill passed by the Senate on Christmas Eve as well as a package of changes.

The Senate bill would then go to Obama for his signature and the companion measure to the Senate, which hopes to pass it within the week.