I'm just curious about how many baggage/luggage screenings take place when I fly from one port (Say PDX) on one airline to another port (SFO), and then having connection with another airline to fly to elsewhere (lets assume Asia), how many bag checks/screenings will take place?

Will it be in the home port (PDX) only and goes through till Asia, or will there be another bag check in the transit port (SFO)? And how many will it take, say when I have 7 transit ports in the US before flying off elsewhere outside the US?

I'm still kind of lingering on my last experience where all my luggage were 'man-handled' by TSA, and wanted to try to request to be present while they check my luggage in either ports of departure before leaving the US just to be on the cautious side of things...