The groups dropping the bombs are required to report how much they're spending where, and watchdogs like Spencer MacColl are tracking it all, reports CBS News correspondent Sharyl Attkisson.
In the final frenetic week before the elections, the "money bombs" tell where the battles are most pitched.
Sheila Krumholz says Democrats are back on their heels.
"The conservative outside groups are forcing Democrats to defend races that they didn't think they would need to be shoring up," said Krumholz, the executive director for the Center for Responsive Politics.
That explains the largest one-day ad buy this cycle, made yesterday by the Democratic Congressional Campaign Committee for $21 million.
Their biggest ad purchases this week are to oppose Republican nominees in two House races: Keith Fimian in Virginia for $1.079 million, and for $848,000.
CBS News Complete Coverage: Election 2010
Conservative outside spenders and its sister group dropped their own money bomb yesterday: $6 million. Most of that's targeting Senate races.
They bought a $1-million worth of ads to oppose Democrat Patty Murray, the incumbent in Washington State, and a million more against Democratic senate nominee in President Obama's old seat in Illinois.
The total ad buys have been going up at a remarkable rate of about $20 million a week. This final full week of the campaign, they're on target to top $100 million for the week.