It helps to have stable bi-lateral relationships between countries that choose to connect their grids and economies. This kind of stability is a good thing. The current instability with long relationships being questioned and falling apart is a bad thing. And where you say cost, I say investment. Because energy is a valuable commodity and being able to buy/sell energy via cables has value.

Most renewable energy investments have decent, easy to calculate returns on investment. That's why this stuff is so popular with investors. And that's also why I don't think current policy changes in the US matter long term. It just slightly increases the time to a return on investment. But you still get a return. So, companies will continue to look at batteries, solar, and indeed cables with or without government support. And even a little bit of tariffs (aka. taxes) won't stop that.