If Trump's numbers are +4 on election day, McSally will probably win. Good thing for Sinema, it seems like an outlier.
Obama had a 60% approval rating in MA when Scott Brown won. Its not that important
Thats not even remotely comparable to this.
The MA special had less to do with the national environment and more to do with Coakley being awful.
Sinema's fate may very well depend on how popular Trump is at the given moment.
Coakleys loss can be attributed more to running in 2 GOP wave years: 2010 & 2014 then her quality as a candidate. She was no more worse a candidate than lackluster Blunt, Johnson, Toomey, etc... They just happen to have better timing than her.