The President and Congress need to demonstrate unity in opposition to Iran obtaining a nuclear weapon. Approving this bill would make that message clear. It's a shame the firefighter bill had to be co-opted, but lawmakers have kept language in the bill to allow for the firefighter insurance change as well.
This legislation would undercut the President’s leverage in negotiating with Iran, and would make it less likely that any agreement is reached. Not to mention, it's pretty sneaky voting on an important foreign policy bill, but doing it under another bill with a completely unrelated goal.