It’s not as much a Romney influence as much as a Mormon Church influence. They have put out the word, Rubio is their sanctioned candidate. Idaho is approx 20% or more Mormon.
Romney’s pull with the Mormon community (worldwide) is exactly why he’s speaking out. The Gope knows the “reach” he can affect almost effortlessly.
That’s what I’m betting, they put Romney out to talk to “everyone” but really in hopes it would be one of those famous “dog whistles” to Mormons in Idaho to become the first speed-bump.