Loyalty is one of those conditional virtues, like courage. It is generally agreed to be a good thing, but if applied to an evil cause, increases the evil. Thus we admire loyalty in those who are on our side politically, but find loyal lieutenants on another side to be sinister - unthinking, dangerous folk. Presidential appointees in particular strike us this way. The other guys are always henchmen, sycophants, a cabal, or other name evoking evil.
Yet everyone wants a friend who believes you even when the evidence looks to be against you, and no one admires a supporter who jumps ship as soon as the going gets tough.
And from the outside, we are always so wise, thinking it obvious when a person should no longer believe.