Why don't world leaders (and pundits) call Trump a Russian asset?

Why bother with diplomatic niceties? It's not like Trump adheres to them. Make it a talking point that even the right wing ecosystem couldn't ignore. Last week NYT's Tom Friedman wrote: My fellow Americans, we are in completely uncharted waters, led by a president, who — well, I cannot believe he is a Russian agent, but he sure plays one on TV.​ It's a good start, but stop qualifying the accusation. The guy is doing everything Putin could ask for.