Overall, the Senate Republicans' party apparatus is advertising in eight states in the final week: Arizona, Indiana, Montana, North Dakota, Nevada, Ohio, Virginia and Wisconsin.
Senate Democrats' party operation is airing ads in those states, too, plus two others: Connecticut and Missouri.
Taken together, the ad wars sketch out a map of where the battle for the Senate is likely to be won.
Whether the late wave of ads can break through the media clutter and provide an edge won't be known until after the polls close Election Day, but some big ad buys are drawing attention:
—American Crossroads, a super PAC organized by Rove, and its affiliate, Crossroads GPS, are making a big push over the final week, flooding the airwaves with $10.5 million in ads airing in Maine, New Mexico, Nevada, North Dakota, Ohio, Virginia, Indiana, Montana, Nebraska and Wisconsin.
—Democratic-aligned Majority PAC is countering with a $7 million ad blitz targeting Montana, Wisconsin, Indiana, North Dakota, Virginia, Connecticut and Florida.
—American Crossroads is pumping $420,000 into Nebraska's tightening Senate race to shore up Republican Deb Fischer as she tries to turn back Democrat Bob Kerrey's bid to return to the Senate.
The closing arguments in ads from both sides are a mixed bag. Republicans cast Democrats as supporters of big government, higher taxes and exploding deficits. Democrats fire back that Republicans are conservative extremists, beholden to special interests and eager to slash key social programs.
Democrats have a 53-47 advantage in the Senate, including two independents who align with them. About a dozen of the 33 seats on the ballot are seen as competitive, most in the West and Midwest. Republicans need a net pickup of four seats to take control if Obama is re-elected, three if GOP presidential candidate Mitt Romney wins, since the vice president gets a tie-breaking vote.