Canada has most of the change in wine exports and is boycotting US alcohol, so modeling them effectively gives you the worst case scenario.

Lets use your numbers then.

Total US domestic sales were about 3.3 billion liters.

Exports were about 253 million liters.

Exports, if they went to 0, would explain less than 8% reduction in wine sales.

But the article quotes a 20% drop.

Exports have decreased maybe 1/3 and that is only in the last 2 years, and that is by your own numbers. That would constitute a 1.5% drop, not a 20% drop.

So changes in exports do not have a significant effect on the numbers, and cannot explain a 20% drop, or even a significant portion of a 20% drop.