A well-connected GOP operative alarmed by the enduring strength of Republican Donald Trump's presidential bid is planning a "guerrilla campaign" backed by secret donors to knock him out of the race. Liz Mair, former online communications director of the Republican National Committee, recently created Trump Card LLC to "defeat and destroy" the celebrity businessman's candidacy, according to a memo obtained by The Wall Street Journal. "In the absence of our efforts, Trump is exceedingly unlikely to implode or be forced out of the race," the Trump Card memo says. "The stark reality is that unless something dramatic and unconventional is...