The extraordinary destruction of a Syrian fighter jet by a US aircraft on Sunday has precious little to do with the Syrian plane's target in the desert near Rasafa - but much to do with the advance of the Syrian army close to the American-backed Kurdish forces along the Euphrates. The American strike on Monday was ... a warning to the Syrians to stay away from the so-called Syrian Democratic Forces - the facade-name for large numbers of Kurds and a few Arab fighters - since they are now very close to each other in the desert. But the Syrian military are still winning against Isis and its fellow militias - with Russian and Hezbollah help, of course - although comparatively few Iranians are involved. The US has been grossly exaggerating the size of the Iranian forces in Syria, perhaps because this fits in with Saudi and American nightmares of Iranian expansion. So who is fighting Isis? And who is not fighting Isis? The Syrian army, supported by the Russians, is fighting Isis. But what is America doing attacking first Assad's air base near Homs, then the regime's allies near Al-Tanf and now one of Assad's fighter jets? It seems that Washington is now keener to strike at Assad - and his Iranian supporters inside Syria - than it is to destroy Isis. That would be following Saudi Arabia's policy. If we are to believe all the Americans now say, they want to destroy Isis but are quite prepared to go on attacking the Syrian government forces that are fighting Isis. Does Washington want simply to break up Syria and leave it as a failed state?