Democrats and Ben Sasse ran out to the mics after reading the whistleblower complaint to claim they were deeply concerned. However, read with caution, others are saying the only evidence is the phone call. The transcript of the phone call is the only available evidence. It relies very heavily on media reports but the media is over 90% lined up against the President.
This is hearsay and the whistleblower heard gossip.
There is a classified appendix that includes information that all assistance to Ukraine was held back.
There is evidence of political bias according to the intelligence Inspector General.
So far this is second-hand information but it will be used as evidence for impeachment, at least in part.