Ohio Senate candidate Josh Mandel has reserved over $4 million in airtime for the last month of the 2012 campaign, multiple strategists tell me.

The Republican state treasurer is running a competitive race against Democratic Sen. Sherrod Brown. The Ohio contest is on track to be one of the most expensive in the country: GOP outside groups have spent heavily there, and the Democratic Senatorial Campaign Committee has purchased over $5 million in TV ads for the fall.

A GOP strategist involved in the race said the buying — about $4.2 million so far — is proof that Mandel will “have the resources to go toe-to-toe down the homestretch with not just an incumbent but one of the most well-funded members of the U.S. Senate.”