GE Monogram--opening door trips circuit breaker

A year ago the internal fuse in our microwave blew, and we replaced it. A few months ago, the microwave started to trip the circuit breaker occasionally when the door was opened, but we just reset the breaker, and it would be fine for a few weeks. Now, every time we open the door, the microwave trips the circuit breaker. Any ideas what might be causing the door to trip the breaker?