Top allies of Senate Majority Leader Mitch McConnell are diving into the midterm elections with an initial fall television advertising reservation of nearly $25 million.

Senate Leadership Fund, financed by wealthy campaign contributors cultivated by the Kentucky Republican, is placing buys in Missouri, Nevada, and North Dakota in a bid to pad the GOP’s thin 51-49 majority. The group plans tens of millions more in advertising to begin after Labor Day, but is delaying to guard its November strategy.