Pssst! Want to see how bad some of the ratings are for incumbent Republican Senators up in 2016?
White -- retiring incumbent, with "D" or "R" for the party in question.
Light green -- Republican incumbent apparently running for re-election, no polls.
Light orange -- Democratic incumbent apparently running for re-election, no polls.
Blue -- Republican running for re-election with current polls available.
Red -- Democrat running for re-election with current polls available.
Yellow is for an incumbent under indictment or impeachment, or who has a terminal diagnosis that likely ends his life before his Senatorial term is up. "R" for Republican, "D" for Democratic. No distinction of shade here.
Intensity percentage shows the first digit of the approval of the incumbent Senator --
"2" for approval between 20% and 30%, "3" for approval between 30% and 39%... "7" for approval between 70% and 79%.
Numbers are recent approval ratings for incumbent Senators if their approvals are below 55%. I'm not showing any number for any incumbent whose approval is 55% or higher because even this early that looks very safe.
An asterisk (*) is for an appointed incumbent (there are none yet, but I predict that there will be one soon!) because appointed pols have never shown their electability.
...Any elected incumbent with an approval rating below 43% should be assumed vulnerable unless there is compelling cause to believe otherwise. At 44% one has about a 50% chance of winning re-election. The chance of winning re-election goes to practically 'prohibitive favorite' around 50% approval and drops off to practically zero rapidly in the zone of 35% approval.
Below 35% approval one has elected pols with extreme problems -- scandal, primary challenges, the bailiwick going sour fast for the pol's party; there's little record on them because they usually resign in disgrace, lose a primary challenge, or decide to nor run for re-election.