“Only the deputy attorney general with fire him. That ... investigation is still going to go on,†Collins said.
Several things:
It was nice of her to tell the future nominee what they "must say" to be approved. Saying what you will do means nothing.
The Senator is way, way, behind the times. Currently there is no "Russia investigation". Even Mueller wants to wrap that up. Now, Mueller is simply 'fishing' and flailing about like the Ghestapo, looking for 'anything' to pin on anybody directly or indirectly connected to Trump or his administration. The investigation as it was chartered is already over. All that is left of it is the death throes of a failed coup attempt.
Theoretically, there isn't supposed to be a litmus test for nominees, in the sense that Congressmen say, "I will vote for you but only if you pre-agree to do XYZ. That's not the way the nomination process is supposed to work. But of course today, with Trump, laws rules and traditions, no longer matter.