Bedtime trouble

We have a bedtime routine we have been using forever, and nothing has changed. Lately, Andy screams for an hour or two when it is time for bed. It has been tough on everyone. He is so angry it is hard to calm him down. I finally got him to go down tonight with a really calm voice telling him it's okay, but it only works after he's been crying for a while. He will be two in a month. Why does this have to be so hard?