For example, if a senator gave a speech detailing why senators needed more money and someone dismissed the arguments based on the senator's sentatorness rather the quality of the argument's themselves.
Also, an ad hominem is not merely a 'personal attack.' For example, an insult is not an ad hominem. An ad hominem is an attempt to discredit an argument based on qualities of the arguer instead of the argument itself. Pointing out a conflict of interest is an ad hominem attack if you are using it to discredit an argument.
For instance: "Why should we give creedence to his position on the origin of the universe? He has been divorced twice and is cheating on his current wife... Surely we can't trust what he has to say."
Here the argument is attack by attacking the person. The attack on the person has no direct translation to the dispute at hand.