What was Moshe's mindset regarding sending the spies? Specifically: He seemed to have his doubts because he blessed Yehoshua by adding the letter "Heh" to his name so Hashem should protect him. Why didn't Moshe try to abort the whole plan and influence the "spies" not to go?
What was Moshe's mindset regarding sending the spies?
The original story in Bemidbar omits a good bit of detail as to what occurred prior to Moshe's decision to send them. This is what the beginning of Devarim completes, to an extent.
Synopsis of Devarim 1:20-23:
G-d tells Moses, "Look, I have given you the land. Go and inherit it!" Rash"i explains that this means that they would not have to fight any wars, because G-d had already given them the land. The people come to Moses and say, "Let's send people to view the land so that they could tell us the best way to go there and the cities we should live in." Moses thinks this is a good idea, and he appoints one man from each tribe.
So, yes, initially, Moses was wondering why they even needed to send anyone to view the land, because, he tried to convince them that G-d had given them the land, and there was nothing to fear regarding the people currently living there.
Seforno commentary on verse 23 says, that since the people said that the purpose to send spies was to discover the best way to get there and where to live, he thought this was really their motive, and, thus agreed to send them.