Jul 22, 2013 - 9:59 AM
You don't need reservations for Switzerland, but you do need them for your trips to and in Italy. You can best order them online, as (the desired) seats may run out as your travel date gets nearer. Since you live in the USA, you can book seats here
. More information about seat reservations can be found here
If you don't have tickets for Italy yet, then don't book just reservations. In that case you'd better book tickets + reservations combined. You can arrange for that from the same website here
. Your Swiss Card covers the leg Mürren to Domodossola, so you only need tickets for Domodossola to Venice (if the system can't find those tickets, try Brig instead, which is one stop earlier).