Starting with the caveats, note that in a "poll-poor" environment such as Portugal, it's understandable that a single poll gets a lot of attention. But let's not forget that a poll is just a poll. And although this last one somehow "feels right" (unlike this one), that does not make it "right" or "wrong," whatever that means when we talk about measuring public opinion. We need more data.
Furthermore, recall that the last Catholic University poll was conducted in late May/early June. This means that the massive PSD drop cannot be assigned exclusively to the measures related to social security contributions: the "Relvas affair(s)" and the privatization of public television were two very contentious issues that preceded the last austerity measures. Finally, note that the poll was conducted not only at the height (so far) of mobilization against the government but also following a week during which PSD figures, employers, unions, and even the minor coalition partners voiced their disagreement with the government's measures. So, although it is always possible that things can get worse for the PSD, it's probably safe to say that they had never as bad as in that period when the fieldwork took place.
Having said that, a few more interesting results:
* In the previous poll by the same institute, the PM was positively rated (getting 10 or more in a 0 to 20 scale) by 48% of respondents. This figure now dropped to 34%, making him the party leader with the worst approval rating.
* 78% of respondents disagree with the notion that the reduction of companies' social security contributions will help fighting unemployment, while 81% disagree with the notion this will have an impact on consumer prices. This is, in a way, a measure of how unsuccessful the communication of this measure was, as well as of the large consensus against it on the part of the kind of sources (media, expert, partisan) people likely used to form any sort of opinion about it.
* In contrast, there is an absolutely massive support for measures that were barely discussed, such as increasing taxes over luxury items or over high value real estate: support is always above 80%.
* 48% of respondents think now likely that Portugal will face a situation similar to Greece in the short-run, against 34% just three months ago.
*60% of respondents believe that no opposition party would do better than the current government if it was in power. Considering that 77% make a negative evaluation of the work of the current government, this helps explaining why, while the PSD drops in this poll, the PS fails to capitalize.