President Trump announced a plan on Sunday night to slap a 100% tariff on foreign-produced films — prompting a slew of questions in Hollywood.

Starting with: Huh?

Runaway production has been debated for decades, and in recent months there’s been a push for federal policy to address it. But nobody — nobody — in Hollywood is asking for a tariff on foreign-made films.

Here are seven major questions left unanswered on Trump’s proposal:

Will he do that?

Trump only said he was “authorizing” the U.S. Trade Representative and the Commerce Department to impose a 100% tariff on foreign films. He didn’t say he would do it. With previous tariff threats, Trump has sometimes made good and sometimes backed off in the face of pressure.

Can he do that?

For previous tariffs, Trump has claimed authority under the International Emergency Economic Powers Act of 1977, which gives the president broad powers to regulate...