https://en.wikipedia.org/wiki/Donald_Trump%E2%80%93Russia_do...
notably: it's not the GOP the organization that initial funded the oppo, but a private news org with conservative leanings. and the FBI did not fund the dossier, but were provided it during its creation. (side note: who cares)
When it comes to corroboration: I would think the special investigation is good enough evidence that the claims of Russian cooperation are being taken seriously, no? Significant is a weasel word but there is actual smoke here.
How would you tell the claims being taken seriously from the investigators trying to use the legal system to get dirt on Donald Trump?
At this point, the investigation has been ongoing for around 10 months, and currently they've only found anything on Paul Manafort, who was Trump's campaign manager for a few months.
The charges against Manafort are essentially failing to disclose lobbying for foreign agents, tax evasion, and money laundering [0]. The lobbying was done while Manafort was working for the Podesta Group, which was founded by Hillary Clinton's campaign manager [1].
On a side note, I find it interesting how Wikipedia doesn't have any information on Manafort's involvement with the Podesta Group.
[0]: https://www.justice.gov/sco
[1]: https://www.politico.com/story/2016/08/podesta-group-paul-ma...
