Within minutes of the vote, the National Republican Senatorial Committee sent out news releases to Missouri, Montana and Nebraska as well as several other states, criticizing the Democrats on their vote and sounding an overarching theme.

"While McCaskill doubles down on her liberal Washington record, Missourians have yet another reason to replace her with a commonsense Republican next year," said Chris Bond, a spokesman for the NRSC.

McCaskill had said earlier in the day that she would vote against any effort to cut off money for the law.

"I voted for the bill and I think there are real cost savings in the bill," she said.

Nelson defended his vote too, saying, "Nebraska's families and small businesses can't afford to continue to pay the hospital bills of those who don't have health insurance."

McCaskill, Tester and Nelson have drawn GOP rivals in states that either trend heavily Republican (Montana and Nebraska) or stand as electoral battlegrounds (Missouri). Freshman Sen. Joe Manchin has no announced foes in West Virginia and remains popular, but his state voters strongly backed Republican presidential nominee John McCain over Obama by 13 percentage points in 2008.

Manchin defended his vote to fund the law, saying in a statement "Democrats and Republicans must work together to keep the good parts and eliminate the bad parts of the health care bill."

In Missouri, the sentiment runs against the law. Voters last year overwhelmingly backed a ballot measure that would nullify the health care law. The margin was 3-to-1. Just this week, Missouri Attorney General Chris Koster filed a court brief challenging the main provision of the health care law — the requirement that most Americans get insurance. Koster, a Republican turned Democrat, endorsed the effort of more than two dozen governors and attorneys general who have filed suit contending the requirement is unconstitutional.

In Montana, a recent poll showed Tester running about even with his Republican rival, Rep. Denny Rehberg. The survey also found strong support for repealing the health care law, with 57 percent backing such a step.

Overall, public support for the divisive health care law has dropped to its lowest level since Obama signed it in March 2010, according to a new Associated Press-GfK poll. Forty-five percent oppose the overhaul, while 35 percent say they support the changes, with a significant drop among independents.

Among seniors, one of the most reliable voting blocs, 59 percent oppose the law, while just 29 percent support it. A narrow majority of seniors — 51 percent — say they trust Republicans over Democrats to handle health care.

"My read, especially from southern Illinois that shares a media market with Missouri, is it is increasingly unpopular, especially with seniors who realize the Medicare cuts in the law," said Sen. Mark Kirk, R-Ill.

Kirk and his Republicans have a legitimate shot at capturing control of the Senate in 2012 despite the Democratic Party's inherent advantages with an incumbent president at the top of the ticket. Democrats must defend 21 seats to the Republicans' 10, including seats open due to retirements in North Dakota and Virginia. The current Senate breakdown is 51 Democrats and 47 Republicans, with two independents who caucus with the Democrats.

Senate Republican leader Mitch McConnell of Kentucky, who would take charge if the GOP wins the Senate in 2012, has pushed for a health care vote.

"The more we continue to talk about the president's health care bill the more we're playing on fertile ground for Republicans," said Brian Walsh, spokesman for the National Republican Senatorial Committee.

In the negotiations last week, House Republicans had wanted to make it even tougher on Democrats. They pushed for the spending bill to include a provision cutting off funds for the health care law, which would have forced Democrats to muster the votes to eliminate the provision. They also envisioned a simple majority to pass the separate measure rather than the harder 60-vote threshold that the White House and Congress settled on.

Senior Democratic leadership aides said Sen. Dick Durbin of Illinois, the No. 2 Democrat, came up with the compromise. On Thursday, he was on the Senate floor defending the law. "I'm open to revisiting health care reform," he said, but "the notion of wiping the slate clean would be a step backward for Americans."

Said Matt Canter, a spokesman for the committee to help elect Democrats: "This is just a complete charade and unfortunate distraction from the real work that's got to get done."