Q1 may start to show some effects, especially for the likes of Tesla who rely ~entirely on sales of big-ticket items to consumers (though I think Tesla's a special case here in any case; Musk's recent misbehaviour would be hurting it even outside the context of an incipient trade war). There aren't actually many US companies in that space with a big European market, though. Apple, maybe, but even then a lot of their sales would be non-consumer.

As you say, big effects for most companies, if they come, will come later.