4) Roll Call reports that Sen. Claire McCaskill, D-Mo., has made a $3 million ad buy on statewide broadcast TV for the final weeks of her campaign. We're going to see more and more of this in the coming weeks, as candidates and campaign committees reserve time well in advance of the stretch run to take advantage if discounted rates. McCaskill has already been up on TV, and in her first spot, she didn't go after any one GOP candidate, instead focusing her offense on the outside groups attacking her. 3) Sen. John Kerry, D-Mass., will stand in for Romney in President Obama's debate prep sessions. Kerry is a good fit; he's been watching Romney for 18 years, the Boston Globe reports. He's also an experienced debater at the presidential level and has felt some of the same criticism currently being lobbed at Romney (flip-flopper, out of touch) directed at him. 2) CNN reports that Restore Our Future, the pro-Romney super PAC, is making a new $7 million ad buy and the Romney campaign is spending almost $3 million on another week of ads in seven battleground states. Restore Our Future recently got a $10 million cash infusion from billionaire Sheldon Adelson, once the main contributor to a super PAC that helped keep Newt Gingrich's presidential campaign afloat. 1) A surprising blockbuster story from ABC News's Jonathan Karl, who reports that Sen. Marco Rubio, R-Fla., isn't being vetted to be Romney's vice presidential running mate. As Karl points out in the story, this doesn't mean that he won't eventually be vetted, but it has been about two months since Romney tapped Beth Myers to lead the search. Rubio's compelling personal narrative, popularity among conservatives, and knack for public speaking has made him a frontrunner for the nod in the eyes of virtually every observer eying the race. So why didn't Romney take a closer look at Rubio? Hotline Executive Editor Josh Kraushaar writes: "In retrospect, the biggest clue that Mitt Romney wouldn't be looking to Rubio took place Sunday, when the Republican presidential nominee awkwardly batted away questions about Obama's executive order on CBS' 'Face the Nation.' It was clear that immigration was the last thing Romney wanted to talk about. Selecting Rubio would only underscore the divide in the Republican party between immigration reformers and restrictionists."