The six most vulnerable senators this year are all Democrats - Roll Call

This is definitely opinion. It is somewhat based on poll numbers and demographics of the named senator's districts, but mostly it's Nostradamus type predictions of outcome in the races, and some "Ripley's; Believe it or not". Maybe you can use the info when you talk to your bookie.
SGT James Murphy, CPT Jack Durish,
SPC Gary Welch, SGT Mark Anderson,
CPL Douglas Chrysler, LTC Trent Klug,
CSM Charles Hayden, SMSgt David A Asbury,
SSG William Jones,
SSG Michael Noll, MAJ Dale E. Wilson, Ph.D.
SGM Erik Marquez, CW3 Harvey K.
SFC William Farrell, CPL Ronald Keyes Jr
Sgt (Join to see), SSG (Join to see)