I don’t think Kerry is under USSS protection. He’s not currently running for President is he? Even so, he won’t have such protection until the primaries are over.
On that point you may well be correct. I caught myself right after I posted that item, but too late! I think that Secret Service protection 'usually' ends after someone is no longer a candidate, but in Kerry's specific case I'm honestly not sure.
I seem to recall that lifetime Secret Service protection only applies to former Presidents, Vice-Presidents and their families and current candidates.