It would be very difficult for Trump to back away from having his AG appoint an ‘independent counsel’ (AKA ‘special prosecutor’), unless he wanted to offer Hillary a pardon.
Note that a president can impose humiliating conditions on a pardon.
In the case of Nixon, his underlings went down while he himself was not prosecuted. There’s some sense in such a situation as it is would-be henchmen that need the real warnings. By the time someone gets to Hillary’s status, they are old and irredeemable.
If Trump doesn’t want to have the Hillary problem as a distraction, he should signal strongly to Obama that she is going down. Let Obama pardon her, not Trump.