One major argument against the US withdrawing from the P5+1 nuclear deal with Iran was the impact it would have on US relations with the other parties to the deal, including European allies. This appears indeed to be the case, as Europe scrambles to strike back against the US measures.
With the US talking new sanctions, and US officials ordering European companies to stop doing business with Iran, the European Union is already discussing legislation that would effectively block the US from enforcing the measure. This legislation is believed to echo the 1996 legislation the EU used to block US sanctions on Cuba from preventing EU business ties.
Since the Iran deal was signed, EU companies have been scrambling to secure lucrative infrastructure deals. The US largely prevented its own companies from reaching such deals, and has tried to keep EU banks from financing deals that had nothing to do with the US. Europe was annoyed at this before, and now that the US isn’t even a party to the deal, they are likely to be even less willing to brook US interference.