'Kill the bill! Kill the bill!' conservative and small government advocates chanted Thursday, some having traveled on short notice from as far as California and Texas to protest what they saw as tantamount to socialized medicine. 'No Marx. No Mao,' one protest sign read. 'No socialized anything,' read another. Democratic leaders, who are making a last-minute push to nail down a majority vote for their overhaul plan, touted endorsements by the AARP and the American Medical Association. The AARP endorsement was prized because the seniors lobby is an electoral powerhouse and has been skeptical of the Democrats' proposals to reduce Medicare spending. The AMA's support marked a turnaround for a group that played a leading role in stopping past reform efforts. The public pressure from left and right provided a dramatic background for a scheduled floor debate Saturday -- with a vote expected later that day. The angry opposition voices echoed the conservative protests that have been heard this year at anti-tax 'Tea Party' rallies, as well as at congressional town meetings on health care and in some of the campaigns leading up to Tuesday's off-year elections. While the rally assembled in front of the Capitol was peaceful, Capitol Police arrested 21 anti-abortion activists and others inside House and Senate office buildings for disorderly conduct and related charges. Some Republicans have tried to keep their distance from the Tea Party movement because of some activists' rhetoric -- such as protest signs seen Thursday linking President Barack Obama and the health care bill to Nazi Germany. Nonetheless, dozens of House Republicans, including their top party leaders, embraced the cause by appearing on the Capitol steps to address the crowd. House Republican Leader John Boehner, R-Ohio, denounced the health care bill as 'the biggest threat to freedom I have seen in the 19 years I've been here in Washington.' The crowd's biggest cheers were for Rep. Michelle Bachman, R-Minn., a first-term icon of grass-roots conservatives who, last week on cable television, had invited health bill opponents to come to the rally and lobby lawmakers. 'You came to your House,' she said, standing at a podium beside a towering stack of paper that was the text of the health care bill. 'You came for an emergency House call.'' No House Republican is expected to vote for the bill, so Speaker Nancy Pelosi, D-Calif., has been laboring to nail down the 218 votes she needs from her own party's ranks. Obama is slated to address the House Democratic Caucus on Friday as part of the final push for votes. Democrats also secured a new vote Thursday when Pelosi swore in Rep. John Garamendi, D-Calif., who won a special election Tuesday. Another special-election winner, Democrat Bill Owens of New York, is to be sworn in Friday. The bill's endorsement by the doctors' and seniors' lobby groups, in addition to support announced Tuesday by the American Cancer Society Cancer Action Network, helps counter mounting opposition among employer groups that are stepping up their advertising campaign against the bill. The 40 million-member AARP has been pushing for a health overhaul for more than a year but had withheld a formal endorsement of any of the bills being developed by congressional Democrats. On Thursday, AARP executive vice president Nancy LeaMond said the group saw the House Democratic bill as the most promising proposal. 'We can say with confidence that it meets our priorities for protecting Medicare, providing more affordable insurance for 50- to 64-year-olds and reforming our health care system,' she said at the group's Washington headquarters. The AMA's endorsement had been thrown in question when Congress delayed action on a related measure that is the group's top priority -- a bill to cancel a scheduled cut in Medicare payment rates to doctors. But Democratic leaders said that issue would be addressed later this year. In announcing the group's endorsement Thursday, AMA President J. James Rohack said, 'The time to make health system reform a reality is now.' He added that the measure 'is not the perfect bill ... but it goes a long way toward expanding access to high-quality affordable health coverage for all Americans.' The AMA's support comes ahead of a policymaking meeting of its House of Delegates in Houston that begins Saturday. The organization is being asked by some constituencies to back away from supporting health care reform. 'These bills go far beyond what is necessary to fix what is broken with our health care system, and they grant the federal government considerable new powers and authority, which could ultimately amount to a complete government takeover of health care, and which is anathema to doctors and patients,' reads a resolution introduced by three associations of surgeons. Staff writers Kim Geiger and Alex Hart in Washington contributed to this report. 