The National Journal's Hotline blog looks into why the Democratic Senatorial Campaign Committee has begun spending heavily for Arlen Specter campaign ads:

Dems backing Specter may be worried that Rep. Joe Sestak (D) is preparing to unleash a slew of late ads in the fortnight before the primary. A new poll released today already shows Specter's decisive lead is sagging; he leads Sestak by a 47%-39% margin, just 4 weeks after holding a 17-point advantage.

Sestak has yet to reserve time for the next 2 weeks, but his most recent FEC report suggests he has plenty of firepower left over. Sestak reported $5.2M in the bank at the end of March, and he's only spent $1.5M on ads so far. That indicates he could outspend Specter over the race's final 2 weeks.

Specter, who had $9M in the bank at the end of the quarter, has already reserved $635K in ads for this week, all on broadcast, and $646K for ads beginning May 11 and running through the May 18 primary. That will equal 1K gross ratings points in every market in PA except Philadelphia, which is getting 650 GRPs, and Johnstown, which gets 700 points.