Why Didn't The Beatles Record in America in 1966?

I was reading a book called, Recording The Beatles:  The Studio Equipment and Techniques Used To Create Their Classic Albums by Kevin Ryan and Brian Kehew (Curvebender Pub., 2006).  The authors had access to the EMI Archives.  They talked about how The Beatles were planning to fly to the United States and record in Nashville what ended up to be the Revolver album.  The authors said that didn't work out and The Beatles stayed in England.  Why didn't they come to America?

In The Beatles L.A. press conference of August 28, 1966, they discussed not being able to record in America, without mentioning when or what album they would have been working on.  You can find the discussion in the Youtube video at:  http://www.youtube.com/watch?v=Irw1OCWp1Gs .  Here is what George and (possibly) real Paul said:

Question:  (1:19-1:22):   Are you ever going to record in the United States and why haven't you yet?
Paul:         (1:22-1:31):   We tried, actually, but it was a financial matter.  A little trouble over that one.
                                      No, we tried, but ahh---
George:    (1:31):           ---Detail and politics---
Paul:         (1:31-1:34):   Hush, hush  [and Paul sucks in his breath to indicate it was a big problem.]
George:    (1:34):           ---and [or no] dice---
George:    (1:35):           No comment.

What financially would have kept the extremely rich and influential Beatles from recording in the U.S.?  It would seem that from the cross-talk between Paul and George they were stopped from coming to America and that politics--read the English government--was involved.  Again, in this extremely important time period of early-to-mid 1966, it needs to be explored why The Beatles were being prevented from travelling where they wanted, when they wanted.