How much will bad grades this semester affect admissions

Applying for the current cycle with generally a pretty good gpa ~3.9, however I forecast this will probably drop down to 3.8 because of some classes that are whooping me. Will likely have a C and a B on my transcript for some major-specific classes

I am under the impression that this is not too big a deal, since admissions look at unofficial transcripts that will not have my finalized grades for this semester, though I am curious if programs can rescind offers if they see that my grades are declining, especially in higher level major courses (suggesting that I may not be able to handle the grad school workload).