The most vulnerable Senate incumbents are socking away huge sums of money in an attempt to inoculate themselves against tough 2010 election challenges.

Senate Majority Leader Harry Reid , D-Nev., for instance, who raised more than $2 million during from July 1 to the end of September, and fellow Democratic Sens. Blanche Lincoln of Arkansas and Arlen Specter of Pennsylvania brought in $1.2 million and $1.8 million, respectively, for their cmapaigns.

Targeted Republican incumbents who raised more than $1 million include Sens. David Vitter of Louisiana and Richard M. Burr of North Carolina.

Among blue-chip recruits in open-seat Senate races, Republican Rep. Roy Blunt and Secretary of State Robin Carnahan, a Democrat, each raised more than $1 million for their Missouri contest.

In Ohio, former Rep. Rob Portman, a Republican, brought in $1.3 million for his campaign, while the campaign of his top Democratic challenger, Lt. Gov. Lee Fisher, raised $621,000.

Illinois Treasurer Alexi Giannoulias, a Democrat, raised more than $1.1 million — impressive, but not enough to beat the $1.6 million raised by the Senate campaign of Republican Rep. Mark Steven Kirk .

In New Hampshire’s open-seat race, former state Attorney General Kelly Ayotte, a Republican, outraised Rep. Paul Hodes, a Democrat.

With almost $2.5 million in receipts, Florida Gov. Charlie Crist led GOP Senate hopefuls in fundraising for the quarter. But less important than Crist’s continued success is the unexpectedly strong showing by fellow Florida Republican Marco Rubio, the former state House Speaker, whose campaign raised $1 million — a sum sizable enough to show that his primary challenge is certainly viable.

Kentucky’s open-seat Senate race features two intriguing primaries on both sides of the political divide.

On the Democratic Party side, Attorney General Jack Conway continues to prove that he’s the better-funded candidate. He ended the third quarter with about $1.7 million in cash on hand to Lt. Gov. Daniel Mongiardo’s nearly $752,000.

Kentucky’s Republican primary looks like it’s going to be an equally cash-draining battle.

Eye surgeon Rand Paul is running to the ideological right of Secretary of State Trey Grayson, the establishment choice. Using the same Internet-based fundraising network that helped his father, Rep. Ron Paul , R-Texas, in his 2008 presidential run, Rand Paul broke the $1 million mark during the third quarter. Grayson raised $645,000 and ended September with $1.1 million on hand to Paul’s $912,000.

Another race to watch is in Connecticut, where Democrat Christopher J. Dodd is seeking a sixth term.