The GOP is set to unleash an attack on some moderate Democrats who voted to begin debate on the Senate health care reform bill.

The Senate voted this weekend to bring the legislation to the floor and now a big  fight lays ahead. Republicans are opposed to the Senate measure and some Democrats also have concerns.

As the fight over health care reform moves forward in Congress, moderate Democrats hold much of the power and a Republican National Committee web ad released on Monday took aim at them.

Saturday's 60-39 party-line vote allows debate to begin on the Senate health care bill, but some who voted in favor of debate say they may not vote the same way in the end. 

The bill includes a controversial government-run, or public health insurance option, which is opposed unanimously by Republicans and by some members of the Democratic caucus, whose votes are crucial to avoid a Republican filibuster. 

The Senate's number two Democrat says it's possible that sticking point could be negotiated. But, Republicans say the bill is a takeover of the health care system that Americans don't want.

- Nicole Collins reporting for CNN.