I didn't see the "campaign" line since there are two "from" addresses shown, and the second one (which I saw first) just says "Senator Ted Cruz", not "campaign". It took me looking at the envelope three times after reading the comments to see that the word "campaign" was on the envelope.

Also I tend to open anything that says "open immediately" regardless of where it's from, unless it's super obvious nothing is wrong. I can always throw it out later. Better safe than sorry.