From USA Today:
"Trump and other White House aides have repeatedly denied any contact between the Trump campaign and the Russian government.
The ties between Sessions' staff and the current White House are many. Trump senior policy adviser Stephen Miller was Sessions' communications director before joining the Trump campaign in January 2016, and former Sessions chief of staff Rick Dearborn was director of the Trump transition and is now Trump's deputy chief of staff for legislative affairs.
..Sessions was perhaps Trump's most loyal supporter in Congress last year, and he chaired Trump's national security advisory committee."
Sessions directly benefited from Trump's questionable election. He gained personally from this apparent collusion, gaining a position arguably more powerful than being a senator, and one from which he could shield Trump from investigation. While there is no clear quid-pro-quo, no evidence so far that Sessions was promised the AG slot, or some other political plum, if Trump won, I think we can consider it implied from the outcome.
As a Trump National Security advisor, the CHAIR of Trump's National Security Advisors, Sessions would know damn well about the efforts of the Russians against the US, from hacking Americans (and not ONLY the DNC) but also in the proxy war in Syria as it relates to terrorism and ISIL. Sessions was much more than "called a surrogate a time or two" in his relationship to Trump and the campaign. He was a key insider, which makes his connections to Russia all the more suspect.
If the DoJ and the FBI can get leverage on Sessions for his conduct -- like perjury -- Sessions might throw Trump under the bus to save his own hide. Not just Trump but also Trump staffer Stephen Miller who is a former Jeff Sessions staffer. Or at least Sessions might try to reduce the punishment from his actions in some way if not seek total immunity. Sessions has never struck me as a particularly strong person who would fall on his sword for someone like Trump; rather he is and has always been something of an opportunist, a man who took more money from special interests like Big Oil to act against the interests of his constituents than any other member of Congress.