It’s impossible to know how large this potential army is, but last October, 41 percent of pro-Trump Americans agreed with the statement that “because things have gotten so far off track, true American patriots may have to resort to violence in order to save our country.” (That view was shared by 22 percent of independents and 13 percent of Democrats.) THE DAY AFTER MAINE SECRETARY OF STATE SHENNA BELLOWS barred Trump from the primary ballot there in late December, her home was “swatted.” As Bellows explained, “That’s when someone calls in a fake emergency to evoke a strong law enforcement...