Dear Bernard
1 thing that Wellington was worried about but is often not mentioned in History books was the Grain supply of his Army by the US. If Madison had decided to cut that, it could’ve seriously damaged his Army as his Letters to Horse Guards attest to l. This article on the subject will be of interest to read on how events in the US affected Spain
Geraint
https://www.napoleon-series.org/military-info/Warof1812/2006/Issue5/c_Wellington.html