I don't think he's anyone's asset per se. Not in his mind, anyway. He's just a dumb, self-serving, immoral, deluded, narcissist who cares only for himself. I doubt he recognises that he furthers the interests of Putin (I reckon he truly believes he is being tough on Russia), but even if he does somehow recognise it deep down he clearly has no capacity for caring for America. It just doesn't matter to him at all.
The biggest irony of all is the idiots who vote for him thinking he's a "patriot". How detached from reality must you be to believe that.