When requested for certain purposes. They cannot simply demand the returns hoping to find something.IOW, it's a tradition that he, for his own reasons, doesn't care to continue, and he doesn't have to. You could ask why it took Obama so long to release his birth certificate, and why he only did it when it became a problem. You could ask why Obama refused to release his school records. You could ask why Hillary wouldn't release her medical records, and on it goes. People still have the right to privacy, even if they run for president. Naturally, the haters and usual suspects jump on whatever is withheld as containing the smoking gun that will allow them to finally "get" whoever it is they're mad at.All Presidents since Nixon have released their taxes and I’m not running for President
There's a law mandating tax returns be turned over to specific House committees when requested. Trump is ordering his staff to ignore the law.