One of 28 days threatening to boycott Trump and co? (6)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

D (days) OMINOUS (threatening) minus (to boycott) US (Trump and co?) Question mark indeed! I guess ‘Pope Leo and co?’ could refer to all the residents of Chicago? Dominoes have blank through six pips on each square. So in ascending order we have 00, 01, …, 06, 11, 12, …, 16, and so forth, up to 66. That makes 7 + 6 + 5 + ⋯ + 1 = 7 x 8 ÷ 2 = 28 dominoes, a fact I did not know until right now. Possibly, you also did not know this.