This is the evidence they will face, especially about the Shokan affidavit.
CNN's Kate Bolduan speaks with former US ambassador to Ukraine John Herbst about testimony he gave before Congress in 2016 about former Vice President Joe Biden's role in fighting corruption in Ukraine.
They would probably need some type of credible evidence in order to investigate a non government US citizen in Congress, which no one has produced it yet.
They have more on Trump's family the Hunter Biden.