It hasn't sunk in yet, but today's indictments are a huge development. For the first time, the Russian effort to interfere, and for the purpose of electing Trump, is layed out. Despite this, Trump is going forward with the meeting with Putin. He also called it a witch hunt again today.
But, it is increasingly clear that the Republicans cannot support Trump's attacks on the investigation much longer. They know that if the investigation shows he is compromised, and a case that they've in some way hindered that, then they'll go down with Trump.
As people discuss and process this in the halls of Congress, there is going to be real panic. Trump will still have their support, but it will be muted, more and more. The risk of being on the wrong side of history here is just too great.
And if after the meeting with Putin Trump announces some sort of concession to the Russians or reiterates the Putin denies interfering? I'm not sure but that they'll just have to abandon him at that point.