How will investors know if there's a full-blown war?

Since the start of 2018, Wall Street has been harried by the threat of the imposition of tariffs on products from some of the U.S.’s longstanding trade partners, with a recent escalation of tensions raising the question: Are we in a full-blown trade war? And, if not, when will investors know?

On Sunday, reports emerged indicating (paywall) that the European Union was threatening $300 billion in fresh tariffs against U.S. products if Trump follows through on his intention to enact 20% levies targeting the trade bloc’s auto makers. President Donald Trump said declaring duties on auto manufacturers were his latest and best weapon to extract concessions from rivals, as his administration studies a proposal to impose 20% levies on imported vehicles.

Meanwhile, Canada tariffs also took effect Sunday, with those measures serving as a response to U.S. metals tariffs.

And some of the first tranche of tariffs, aimed at $50 billion in imports from China and designed to punish Beijing for alleged intellectual-property violations and technology theft, will be implemented July 6, with an expectation that China will respond in kind.