Swamped

You're still not convinced that the portal is being used as a weapon; there's a real chance that disrupting this spell could cause a worse outcome than whatever it is the wizard is intending. The tough but logical thing to do is to confront the wizard and demand an explanation, but confront in such a way as to minimize risk to the party.

Having the silver bomb as a plan B makes you feel better about your odds, in case the wizard truly intends harm.

Meanwhile... does it smell like rain?