Okay, I figured out that the combo box was bound to a field, but when I unbound it it stopped operating as a drop down box (of course).  I was trying to get the combo box to act both ways, but it doesn't appear that's possible. I guess I'll have to decide on which way I want to search a field.

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Reply from Alex Hedley:

Tom, up binding it doesn't remove the data source.
You can set the combo to have a Row Source of a Table/Query or a List.this will usually be a Key Column and a Text to display.
You then usually bind it to a Field that the Form has set. i.e. A number field so you can create your relationship.

When using a combo as a search tool you keep the record source the same but isn't of binding it to a Field on your Form you leave it unbound and use the value of that In your search criteria.