If your only reason for attending SDSU at this time is to preserve it as a safety option, I don’t think you have to. Transfer admissions there, from CC, are very straightforward, and you would have to mess up something very badly at your local CC, to lose the option of continuing to SDSU in the event that you don’t get into UCSD or another option you like better. Political Science is an impacted major, but not heavily - the GPA threshold for fall transfer applicants (referenced here: Minimum GPA Requirements | SDSU) is only 2.4 - and the bump you’d get for being local brings that down even more. It doesn’t sound to me as if there’s any real risk of your not making that cut.
The other question is whether there’s anything else you don’t want to miss out on, by foregoing first-year matriculation to SDSU. Were you planning to live on campus? Would you be in the Honors College? Are there particular EC’s that you’d participate in? There’s always the chance that you would like it better than you expect; and a lot happens socially in your freshman year. Academically speaking, a lot of lower-division classes will be substantially the same at CC vs. SDSU, and class sizes will likely be smaller at CC; although if you’re in Weber Honors and would have honors-specific versions of those classes, that could be a point in favor of taking them at SDSU.
But if you’re truly intent on UCSD, it sounds like you’d have a strong chance, if you keep up your high CC GPA; and it’s true that applying as a CC student would be more advantageous than as a CSU-to-UC applicant. And as a backup, you could land at SDSU either way. So really, the question is whether the value of the first-year experience at SDSU is worth giving up, to go all-in for the UC transfer.
Would you be able to be in a honors program at the CC? This can be a help in terms of UC transfer.
I hate to encourage you to pass up SDSU, as I suspect it would be a much better experience than you anticipate… but if your only reason for attending is to preserve the transfer option, there’s no need.