The Constitution sets the senate term at 6 years. There is nothing in it that says '6 years unless...'. Recall of a Senator is unconstitutional. The 10th Amendment doesn't apply.
Alaska, Arizona, California, Colorado, Georgia, Idaho, Kansas, Louisiana, Michigan, Minnesota, Montana, Nevada, New Jersey, North Dakota, Oregon, Rhode Island, Washington, and Wisconsin are the states with some manner of recall availability on their books.
State officials only.
Where is recall of a US senator unconstitutional?