Bridge.begin() stops Serial1!

I'm trying to send a message from Serial1, through the bridge, to a python script.

The program runs correctly in two halfs: One that receives the message from Serial1, and the other that sends a hard-coded message to python through the Bridge to python.

They work fine separate, but when I add Bridge.begin() to the Serial1 half, Serial1 seems to stop working!

Can anyone tell me why this is happening?