GOP's war for eyeballs

Republicans are starting to trounce Democrats in political spending across the Senate map, and that advantage is now showing up in one of the metrics campaigns care about most: impressions.Why it matters: Money matters in a campaign's closing weeks, but what campaigns are ultimately buying is voters' attention — and the price varies, depending on who is buying and when they place their ads.Beginning in September, campaigns and super PACs start competing for the same finite supply of advertising inventory. But the campaigns are guaranteed lower rates.Republicans are generating substantially mor