Supremely confident in their chances of defending the seat, Senate Republicans have cancelled $4 million in television ads for Marco Rubio in Florida in order to pour more money into four Democrat-held seats in California, Illinois, Pennsylvania and Washington. National Democrats meanwhile maintain they will hold on to the majority in the Senate and say Republicans are wasting their money.

The moves reflect a battleground that is constantly changing, but suggests Republicans are playing offense in Senatorial elections this season, while Democrats have been forced into a defensive crouch, protecting the seats they need to maintain a slim majority.

GOP officials say the NRSC will send another $1.8 million to California, where Carly Fiorina is in a tight race with three-term incumbent Democratic Senator Barbara Boxer. That brings the total the committee has devoted to the race to the state maximum of $4.8 million in coordinated money.

Republicans are also putting another $2 million dollars into Illinois where President Barack Obama's former Senate seat has become one of the closest races in the country, with GOP nominee Rep. Mark Kirk and Democrat Alexi Giannoulias deadlocked in the polls. The NRSC has now dropped $4 million total into that contest.

The GOP is also sending $1.3 million additional dollars into Pennsylvania, for a total of about $3 million. The polling in the Keystone state shows the race is neck and neck with Democrats now backing Sestak after a bruising primary campaign against incumbent and party-switcher Democratic Sen. Arlen Specter.

These moves come as Senate Democrats curtail spending in battleground states like Missouri to concentrate assets on the tough races they need to hold onto the majority such as Nevada, where Senate Majority Leader Harry Reid finds himself in a tight race with Tea Party candidate Sharron Angle. Money is also coming into West Virginia from national Democrats where Governor Joe Manchin is trying to hold off Republican businessman John Raese. Raese was beginning to close in on the governor, but Manchin has now pulled ahead in recent polls.

National Democrats counter that they are polling very well in California, Washington, Illinois and Pennsylvania and are spending money in Kentucky, where Democrat Jack Conway is matched up against Tea Party Republican Rand Paul. Kentucky also marks one of the only Democratic pickups still realistically on the table.

National Democrats haven't spent any serious money in Ohio, New Hampshire or Florida in months, with Republicans leading the polls in those states.

However, the Democratic Senatorial Campaign Committee just announced its best third quarter fundraising on record, raking in $27 million over the last three months. DSCC officials tell Fox News they are literally making decisions daily and hourly about where to spend money and many of these races are by no means off the table.

Jake Gibson is a producer working at the Fox News Washington bureau who covers politics, law enforcement and intelligence issues.