US could order one of the Russian consulates closed, but Moscow would likely follow-up by further reductions in permitted US staff
The Russians have 455 diplomatic staff in the United States. The Americans had until recently 1210 diplomatic staff in Russia.
When the US seized properties of the Russian embassy and expelled 35 of its diplomats this left Moscow in a position where it could deliver a far more devastating blow.
By ordering the US cuts down the size of its mission to 455 people it de facto expelled hundreds of US embassy staff.
However, where the Russians needed 455 people to run one embassy and four consulates, the US needed 1210 people to run one embassy and just three consulates. (Russia offered the US to open a fourth consulate but the Americans declined.)
Applying the new principle of parity against Russia the US could now demand Moscow likewise cuts down the number of its consulates to three.
This is exactly the scenario anticipated by some in the Russian press and possibly the foreign service:
According to Kommersant, one of Russia's biggest business dailies, Russian diplomats said that they were told that one of their four consulates is on the chopping block. This makes sense because the U.S. has three consulate offices in Russia, including its Embassy in Moscow. Russia, meanwhile, has four consulates.
This would be a clever way to strike back at the Russian mission if it is so inclined, however, the success would be only temporary. If the Russians accompanied the closure of one of the consulates with a reduction in their staff — which they almost certainly would — then they could demand the US reciprocates and cuts down its 455 staff further.