Lafayette did not grasp how deep, probably irreconcilable, the differences within France had become. As Matteo pointed out, he was an important figure in the early stages of the Revolution; but when he accepted a commission from Louis XVI to be head of the whole nation's Guard, he didn't understand that the mob now viewed him as another tool of the aristocracy while the court still thought of him as a traitor that it was presently impossible to execute.
In order to ride the wave of revolution, Lafayette has to reach the conclusion quickly that Louis XVI is no longer a legitimate monarch. And there is very little basis in L's upbringing for such a radical conclusion.
Perhaps you could take the decision out of his hands, since he's so certain to botch it, and have L16 murdered or incapacitated.