I don't follow Chuck Grassley all that closely, but to me he usually seems above the typical partisan lies and distortions.
That said, this is the EXACT same thing we saw during Trump with anonymous never-identified whistle blowers claiming "evidence" that was never produced.
And not to remotely compare Grassley to Schiff or Swalwell, but those guys went on the news dozens of times saying they had seen evidence proving Trump belonged in jail. That was a lie.
I think there's no question Biden was selling influence, which a lot in the swamp do and it's not necessarily illegal. But before making the leap to saying he accepted a bribe, I'm going to need to see some hard evidence.