Lots of commotion internally in Denmark while the reaction would be decided upon in Washington.
I don’t think Russia wants to retaliate so directly though. As I see it they have very little to gain from taking that bait. More likely acts of retaliation would be plausibly deniable cyber attacks or supporting some proxy in attacking Danish interests abroad. If I was a Danish troop in Iraq, I would be watching my back after this.
Someone I knew was living in an old building with old-timey fuse boxes placed outside the apartments. When she got tired of her idiot neighbours partying on a weekday night for the millionth time despite being asked to dial it down she finally had enough and went to the fuse box and took away all the fuses to the neighbour’s apartment.
She never had trouble with noise again.