if it is, in fact, best they have so far then they are in trouble
It's not the best "they" have so far, barbos. It's the best (most obviously indicative of Trump's guilt) that "we", the public, have so far.
You have no better idea what "they" (the investigators) have so far, than does WP. But rest easy Comrade - even if Russia is found to have done what they did, there will be no repercussions for the Kremlin under the current US regime. They might even try to do away with the Magnistsky act, if they can get it done before impeachment proceeding commence.