Associated Press/Pablo Martinez MonsivaisPresident Donald Trump's terrible, horrible, no good, very bad summer vacation has sent the administration reeling. With 15 months to go before the mid-terms, the White House still has time to recover, but it is not too soon for Trump's political advisors — if they can pull themselves away from their backstabbing and infighting — to ask a painful question: how vulnerable is Trump to being "primaried"? No sitting president in the modern era has ever been successfully "primaried" — meaning that he ran for and lost his party's nomination to run for a second term.