If Flake and Corker really wanted to serve their country they (and perhaps three or four others) would have crossed the floor and joined the Democrats, at least until Trump is gone.
.
Merely announcing that you are quitting doesn't get Mitch McConnell out of the speaker's chair; and it doesn't oust Chuck Grassley as chairman of the judiciary committee.  Those are the steps that are necessary.
.
Furthermore, if Flake and Corker really mean what they say, then they should run as independents in the upcoming elections.  That is what would end te leverage of the Steve Bannons of this world, and allow sanity back into US politics.