The U.S. and South Korea made a serious mistake in canceling a long scheduled military exercise named Max Thunder this week. As the Wall Street Journal reports, the exercise was canceled after South Korea “expressed concerns” over North Korea’s threat to withdraw from the June 12 Singapore summit between President Trump and Kim Jong Un.

In my view, that threat was a bluff designed to test Trump’s willingness to play hard ball in the upcoming negotiations. Unfortunately, Trump blinked. The president’s much-vaunted willingness to “walk away” from negotiations seems to have escaped him on this occasion.