If that's "a flood," you must live in a very dry place.
A. He wasn't president at the time.
B. While it's natural to assume that a candidate is aware of, and is ultimately responsible for, everything his campaign does, I've distinguished between his campaign colluding and Trump personally colluding.
C. Everything that has already been made public about the campaign makes further claims that are less well documented not extraordinary.
> poor and circumstantial evidence that's hard to sort through and falsify
Allow me to spoon-feed an important part to you. Don Jr. publicly released emails about the Trump Tower meeting, those are real and not circumstantial evidence in his desire to collude and others in the campaign attended the meeting with foreknowledge of this. Google 'don jr "i love it"' and there are a zillion news stories about them, I don't know how you missed them at the time. An NPR story linked to a complete PDF [0] of what Don Jr released. Here's the beginning of a NY Times story [1] about them:
> The June 3, 2016, email sent to Donald Trump Jr. could hardly have been more explicit: One of his father’s former Russian business partners had been contacted by a senior Russian government official and was offering to provide the Trump campaign with dirt on Hillary Clinton.
> The documents “would incriminate Hillary and her dealings with Russia and would be very useful to your father,” read the email, written by a trusted intermediary, who added, “This is obviously very high level and sensitive information but is part of Russia and its government’s support for Mr. Trump.”
> If the future president’s eldest son was surprised or disturbed by the provenance of the promised material — or the notion that it was part of a continuing effort by the Russian government to aid his father’s campaign — he gave no indication.
> He replied within minutes: “If it’s what you say I love it especially later in the summer.”
[0] https://s3.documentcloud.org/documents/3892196/Donald-Trump-Jr-Email-Exchange.pdf
[1] https://www.nytimes.com/2017/07/11/us/politics/trump-russia-email-clinton.html