There are at least two things off with your search. First of all, the search you posted has invalid syntax here: | eval Caller_Location=...
by Caller_Location,... My guess is the post is just missing a stats or something similar there. However, a few lines after that, you're trying to eval the fields rdest and Called_Country_ID, this time to the value of fields called _rdest and _Called_Country_ID which aren't present at this point, so rdest and Called_Country_ID will also be null after this. If you want to have an underscore-prefixed field in your table that is available for drilldown, but not shown to the user, you need to do it the other way around: some search
| stats count by Caller_ID rdest
| eval _field_for_drilldown = Caller_ID + " (" + rdest + ")"
... View more