Trump-Putin Meeting: How Will Republicans React? - The Atlantic :

There are exactly two possible explanations for the shameful performance the world witnessed on Monday, from a serving American president.

Either Donald Trump is flat-out an agent of Russian interests—maybe witting, maybe unwitting, from fear of blackmail, in hope of future deals, out of manly respect for Vladimir Putin, out of gratitude for Russia’s help during the election, out of pathetic inability to see beyond his 306 electoral votes. Whatever the exact mixture of motives might be, it doesn’t really matter.

Or he is so profoundly ignorant, insecure, and narcissistic that he did not realize that, at every step, he was advancing the line that Putin hoped he would advance, and the line that the American intelligence, defense, and law-enforcement agencies most dreaded.

Conscious tool. Useful idiot. Those are the choices, though both are possibly true, so that the main question is the proportions.