You can spend a great deal of time trying to run down the origin of the phrase "Useful Idiot" and come up with... not much that is conclusive aside from the attribution of the phrase to Lenin. Lenin did NOT coin the phrase (though there is a Russian equivalent whose meaning has changed somewhat over time).
Useful Idiots are perhaps better understood as a naturally occurring phenomenon, observed and described in similar terms by many people in different places. Who is useful and what is idiocy are subjective determinations that are both relative to the observer and liable to change over time. What is constant is that some people find other people's idiocy to be more or less useful.
Getting right to the point: do Donald Trump and his most ardent sycophants and supporters serve as Useful Idiots for the Kremlin? If - like many of us - you view the Trumpniks as a profound threat to traditional American values, democracy, and the rule of law, then yes, they are indeed idiots. And clearly anything that weakens the United States, either internally or globally, is useful to a revanchist Kremlin that continues to view the United States as the main adversary.
This could of course change. In the event of a rapid disintegration of the Trump administration, the people who replace it may be profoundly hostile to the Kremlin, and may be capable of effectively countering Kremlin actions. The useful idiots of today become quite useless tomorrow, and evidence of collusion between the Kremlin and their current crop of Useful Idiots becomes a weapon to be deployed against the Kremlin.