I doubt that any evidence will ever be enough for republicans, I expect that they would just move the red line again, they know that Putin's Russia is their ally too.

I can only see evidence that is really salacious or visceral work, something like Russia's 1980s kompromat on Trump for example. Everything else would need a bit of explaining and the right wing media would then be able to muddle it.

Trump's presidency was such a travesty, that without Roger Alles successful transformation of the media landscape, no other politician could have been seen to support Trump. But since Roger Ailes media plan has been brought to fruition, republicans know that facts are now optional.