another +1 for adding to your Delta wallet under "Stored Payment Methods".
I scan my boarding pass and I'm in - it's worked 100% of the time. (and CLEAR used to work before that broke)
Note that I have both Delta AMEX Platinum -and- the Platinum Card, yet the Platinum (charge) Card is the only one that shows in my wallet... The Delta one is a separate area under SkyMiles - "Delta SkyMiles Platinum Card Member".
Confusing.