That’s only what Trump has said publicly about Flynn. Trump reportedly hired Flynn despite a post-election warning from President Obama. Former FBI director James Comey testified that a day after Flynn was fired, Trump told him, “‘I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy. I hope you can let this go.” Flynn also claimed that Trump sent him a message in April telling him to “stay strong.”
While Flynn’s lying is ostensibly what prompted his firing, Trump has consistently portrayed his former adviser as a good person who made a mistake, and is now being unfairly dragged through the mud. Suddenly accusing Flynn of being a deceitful opportunist the moment he says something negative about Trump isn’t a very convincing strategy. On the other hand, it should be enough to satisfy those who already believe Mueller’s investigation is a sham, and the Trump team might not have a better option.