He doesn’t dare. Like Rush said...he’d have to have all his meals tested...and would have to hire someone to start his car for him every time before he gets in (shades of The Godfather). I’ll go a step further and speculate that Hillary will be mad (and bitter) enough to give him that concern regardless of his VP pick.
He could just use her to win the election, then dump her. They’re Democrats, they do this irregular stuff naturally.
She’s got some sizeable percentage of the party, and he needs at least all the Democrats, to win.
After that...pick a scandal, any scandal. Put on a grim face and say that she’s not the Hillary he knew, and with deep regret he must accept her resignation.
Rush was joking but we know that Obama would be a neutered duck straight away with those Clintons running around giving him advice and restoring their contacts in every dept (the people Bush never fired)