Instead, it's attacking the Syrian army precisely because it has been defeating ISIS and other jihadi forces, and regaining its own territory and control of its own border with Iraq. The U.S. does not want that to happen. At the very least--if it cannot immediately engender that massive offensive to overthrow the Baathist government--the U.S. wants to control part of the border with Iraq and to occupy a swath of eastern Syria. It wants to establish permanent bases from which to provision and protect jihadi armies, achieving a de facto partitioning of the Syrian state, maintaining a constant state of armed attack against the Damascus government, and reducing Syria to a weakened, rump state that can never present any effective resistance to American, Israeli, or Saudi designs on the region.
This is extremely dangerous, since the Syrians, Russians, and Iranians seem determined not to let this happen. Consistent with his own incompetence and his admiration for tough guys, Trump seems to have abrogated authority to his generals to make decisions of enormous political consequence. Perhaps that's why aggressive actions like the shoot-down of the Syrian plane have been occurring more frequently, and why it's not likely they'll abate. There's a dynamic in motion that will inevitably lead each side to confront a choice of whether to back down, in a way that's obvious, or escalate. Generals aren't good at backing down. A regional or global war is a real possibility and becomes more likely with every such incident.
Though most American politicians and media outlets do not want to say it (and therefore, most citizens cannot see it clearly enough), such a war is the objective of a powerful faction of the Deep State which has been persistent and determined in seeking it. If the generals are loath to back down in a battle, the neocons are adamant about not backing down on their plans for the Middle East. They will not be stopped by anything less than overwhelming popular resistance and international pushback.
The upside of these attacks on Syrian forces is that they wipe the lipstick off the pig of the American project in Syria. It's a regime-change, nation-destroying war that has nothing to do with democracy or human rights, and everything to do with the anti-democratic, chaos-creating designs of the most nefarious regimes in the region and the world. Everyone--European countries who profess concern for international law and stability, and the American people who are fed up with constant wars that have no benefit for them--can see exactly what kind of blatant aggression is unfolding, and decide whether they want to go along with it.
In that regard, any self-identified "liberal" or "progressive" American--and particularly any such American politician--who spent (and may still spend) their political energy attacking Bush, et. al., for that crazy war in Iraq, and who goes along with, or hesitates to immediately and energetically denounce this war, which is already underway, is a political hypocrite, resisting nothing but the obvious.
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