Grand Jury is still active because their are still on going cases. Again, Roger Stone is an example. While the case is active, releasing the entire report could jeopardize any case in trial or pre-trial. The grand jury will remain until the affairs of Muellers investigation are in their disposition phase. Cases handed off to state prosecutors are separate from any federal investigation. States are capable of empaneling their own grand jury's.
It's certainly probable and likely quite a few leaks came from the white house. I have yet to see where that has been confirmed. I'm not talking about those, I'm talking about pre-empitive leaks to the media that shaped the coverage of the investigation the last 2 years and resulted in that video. I'm talking about leaks no one else would know about besides Muellers inner circle or their staff.
A judge certainly could. He/She would have to weigh doing long standing damage to the investigatory bodies, intel community, sources, methods, pave the way for an appeal and re-trial for any active case being tried by the grand jury, open up the grand jurors to harassment and media scrutiny, while simultaneously potentially releasing exculpatory evidence vs waiting 2-3 weeks for the report to be redacted and then at that time weighing the public interest against what hasn't been released. If these are GOP talking points, then they are logical and rational ones. Even a broken clock is right twice a day.
I agree with you the Trump tower meeting is suspicious to say the least. However, the statute for conspiracy is very clear, broad, and has an extremely low threshold.
Telling my tax accountant I'm not going to pay taxes is an example of how low this threshold is
https://www.law.cornell.edu/uscode/text/18/371
Despite what we know about the meeting 19 lawyers who were assisted by a team of approximately 40 FBI agents, intelligence analysts, forensic accountants, and other professional staff didn't find evidence that surpassed that threshold by a reasonable doubt despite the Special Counsel issuing more than 2,800 subpoenas, executing nearly 500 search warrants, obtaining more than 230 orders for communication records, issuing almost 50 orders authorizing use of pen registers, making 13 requests to foreign governments for evidence, and interviewing approximately 500 witnesses in conjunction with any potential evidence acquired during the counter intelligence investigation prior to SC Muellers appointment.