Senate Update:
The name of the game is ad spending. Republicans in particular are starting to sound the alarm over the possibility of running out of money in the final 2 weeks. The blame is falling on big-money outside groups. The GOP is still flush with unprecedented Koch money and Rove's groups are picking up their activity but the party is concerned that other groups aren't helping out. The Kochs started with an unheard-of $40 million ad barrage and have continued to advertise but much of their focus has been on building infrastructure in critical states. Republicans have long trailed Democrats in this area but the Kochs are ponying up the money to try to close the gap moving forward. Early returns, in NC at least, are not very promising. [See:
http://www.newsobserver.com/2014/09/25/4181779_voters-mailed-incorrect-information.html?sp=/99/102/105/&rh=1]. Republicans were going to have to invest in this critical resource one of these years but there might be some growing pains.
The ad spending in September tells us a lot about the state of play. This graph breaks down the activity:
Many things on the graph gel nicely with what we already know, including how the GOP's spending advantage in AK/AR/CO/IA helped their candidates pull even or slightly ahead in those races. We can also see why the GOP is scrambling ferociously to save KS: Orman controlled 80% of the spending. An important note on GA and KY: the Democrats had a big advantage (GA) and reached parity (KY)
on the strength of campaign spending alone; allied outside and committee groups aren't spending here. That could be really significant in the end because the Democrats drew significant GOP resources into races they were always underdogs in.
This is where things stand, at present, for ad time reserved for the final six weeks:
You can see why (and where) the GOP is concerned. The massive $9 million reservation made by the DSCC for NC gives Kay Hagan a massive advantage the rest of the way. Expect a lot of the late-buy GOP money to go here to try to push the numbers as far towards parity as they can be. The Democrats also flip the edge in IA/CO back to their favor. It's a good bet that the GOP will make expensive late-stage buys here, too. Parity in AK/AR means that the races will be decided by GOTV and the ground game unless one party decides to mortgage future (or other) races to try to buy a late edge here. The massive advantage in GA is still solely the work of Nunn's campaign, but it's apparent that the Democrats are not prioritizing KY as their will be no support for Grimes' campaign the rest of the way.
LA is a special case as I have outlined many times. The Democrats have a massive advantage from now until Election Day, but the GOP has stockpiled money for the eventual runoff. Each party is trying to accomplish something different in that race, hence the big disparity.