You are correct that a senator cannot be RECALLED by his state because Senator is a federal position. You’re also right that AZ was working on recalling him when 9/11 happened and a recall in AZ was dropped in the interest of “unity”.
Freepers in AZ were active in leading that effort. Back in those days our federal elected officials signed a paper that they would honor (ha!) the recall if it ever came. I wasn’t here yet, but planning to move here and I thought then that it could be done but I’m resigned to the fact that we can’t vote him out. Not pleased, just resigned. I despise him!
Had it not been for the Seventeenth Amendment, ratified in 1913 when Woodrow Wilson was president, a state would have the power to recall a senator via the state legislature. Since the Seventeenth Amendment's ratification, the U.S. Senate is elected by the popular vote of the masses (far too many that have little or no understanding of political issues), exactly as the U. S. House is elected, the only difference, beside the terms of service, as you know, is that there are the 2 senators (as you know) elected from each state regardless of population, instead of representation by population in districts.
I know that even the state legislatures are flawed, but the officials I know here in (from purple to blue) now liberal Colorado are very politically savvy. But just as an example (and there are many more, I'm certain), no way could I believe that the Minnesota state legislature would ever elect a goofy imbecile such as Al Frankin. I can't possibly imagine that any state legislature, where most members are very politically savvy, electing a political idiot such as that.