Can I wear my civil air patrol uniform here?

For sure! I think it would give the congressman the impression that you are a respectable person without even knowing anything about you. You earned the right to wear that uniform, so definitely wear it proudly. It may help open up small talk dialog about your Air Force career which then relates to the reason for you meeting with him. The uniform will help to tie everything in nicely at the meeting. I'm not in the military, but I'm a female that goes all out with my outfits, especially for special occasions. I have a rule that I live by.... I always dress to the nines at an event-- those who see me and didn't dress up WISH they did. I don't ever want to be one of those people saying, "OMG, I wish I dressed up better!" Definitely go all out with your uniform!! Good luck :)