Is smoking weed bad for asthma?

Yes.: Not to mention a whole bunch of other things it's bad for.

Yes: Smoking (inhaling smoke, which is full of lung irritants and cancer-causing chemicals) of any kind is unhealthy and bad for asthma patients. Weed is illegal under U.S. Law, so one can be thrown in jail and/or convicted of a crime. Jail has its own dangers such as getting assaulted. However, if one's doctor has prescribed weed as a medical treatment, the risks and benefits will have to be compared.

Yes: As this becomes legal, you'll want to find out whether you can tolerate it. I'd much rather you do this (if the law allows) than get involved with tobacco. You may consider some other route of delivery as well. Best wishes.