Mueller handled George Papadopoulos very intelligently. He arrested Papadopoulos quietly and leaned on him to get him to flip before anyone knew about the arrest. Why? Simple. If Trump had gotten any whiff of the arrest, he could have just pardoned Georgie-poo, in which case Mueller would have had nothing to offer the little punk. Mueller's deal required having the threat of more serious charges without Papadopoulos's cooperation. A pardon would nullify that threat.
The reason I keep asserting that Flynn is probably going to be fine in my "How fucked are they?" ratings is that I think he can probably count on a pardon, not just because Trump counts him as basically family*, but because if Flynn testifies against Trump, the jig is up.
One of the arguments I keep encountering, though, is that Trump can't do this because once people are pardoned, they no longer have any legal liability, and hence lose their right to claim the 5th Amendment. They can be compelled to testify. So, if Trump pardons Flynn, Flynn can be compelled to testify against Trump because he wouldn't expose himself to any legal risks in the process!
But, by whom would he be compelled to testify? Remember that a sitting president can't be brought up on criminal charges. A sitting president has to be impeached first, and that ain't gonna happen. But Congress can force Flynn to testify, right?! There's no fucking way in hell that congressional Republicans are going to compel Flynn to testify. The whole point of my argument that impeachment won't happen is that congressional Republicans want to avoid the 1974/1976 electoral sequence by downplaying any scandalous information. Flynn's compelled testimony could expose damaging information. So... why would congressional Republicans compel his testimony?
They wouldn't, and they won't. If Trump pardons anyone to keep them quiet, and congressional Republicans compel their testimony, it would make non-impeachment look bad, and their goal is to avoid impeachment. So... who the fuck in the Republican congressional delegation is going to compel the testimony of anyone Trump pardons? House Oversight Chair, Trey Motherfuckin' Gowdy?! No. Just... no. He'd much rather spend a few more years talking about BENGHAZI!!! Or maybe Hillary's emails or Uranium One or anything but Trump's Russia problems.
OK, so what if Democrats take control of at least one chamber in 2018, and one of the chairs tries to compel Flynn's testimony. He'll show up, and lie. Even if you can catch him in a verifiable lie, and try to charge him... that's back into the criminal system, and Trump can pardon him for the perjury.
The presidential pardon is an incredibly powerful tool. Anyone looking for a way that it could backfire on Trump is engaged in wishful thinking.
*Not the kind he wants to bone, like Ivanka, but the kind he wants to protect, like his idiot sons. Speaking of them, why doesn't he want Jared in prison to get the competition out of the way? Just sayin'...