it's worth remembering that much of the invisible primary is, well, invisible. Conversations happen behind closed doors that we're not privy to. And one difficulty Rubio has faced all year — for several years, really — is that politicos in his home state have spread lots of salacious — and completely unsubstantiated — rumors about him.

A new book claims that Jeb Bush's allies have been spreading rumors about Rubio

Since there's no evidence that these rumors about Rubio have any truth to them, the mainstream press has tended not to mention them in print. But a whisper campaign like this could well lead GOP elites to be hesitant to fall behind Rubio for fear of a looming scandal.

McKay Coppins of BuzzFeed News provides a glimpse into this process today, in an excerpt from his new book The Wilderness. According to Coppins's account, Rubio's team has fought to bat down two rumors that are particularly persistent: one involving an affair, and another that Rubio is "hiding a secret second family." Coppins reports that allies of Jeb Bush tried to prevent Rubio from running in the first place by "circulating the rumors anew among donors and politicos," and that they "tried to convince a number of influential figures in political media that they had the goods on Rubio."

To be clear: There is absolutely nothing to substantiate any of these rumors....