Syria & Iran Have A Reason

So, Syria and Iran have publicly announced they will stand together against the US:

Iran and Syria announced a common front against the United States yesterday as Washington ratcheted up its pressure on two of the countries highest on its list of rogue states.
[...]
Neither country elaborated on what the common front would entail...

But they are only confirming what everyone already knows, and, with no further details to add, merely confirm their de facto alliance, the public deniability of which may have been of use to them had they said nothing.

Leaving the q: why make this announcement at all? To shore up support, perhaps? Or to provide cover for joint domestic operations where each country helps to suppress the dissdents of the other? Iran has done that before: bring in foreigners to put down demonstrations and, in general, press the heel of the mullahs' boot down on the populace.

Whatever the reason, there is a reason. An announcement like this doesn't just happen w/out one.