This is interesting. I could have sworn that I saw a poll on FOX News while I was eating lunch that measured the same thing and it was more like 30%-30% Dems-Reeps have a clear vision or strong plan for America. That may be because other options included "No opinion" and "Don't know."
Croaky, polling questions could be very suspect. In your recollection, you have the addition that it is or could be a "strong" plan. Many may doubt the GOP on that point but think the Dems just have no plan... Could explain it.
Granted, wording matters. I'd be curious to see the difference between the two questions.
Also - could be that the Fox one asked which one is better; while this asked if they do in the first place. (Notice this one adds up to more than 100%)