Forces in the Syrian conflict backed by the United States and Russia are drawing ever closer to one another, and closer to a dangerous clash. The United States and Russia are backing opposing sides which are now both racing toward the Iraqi border, and the deconfliction channel established to prevent clashes between them is being put to the test. After weeks of accusations of attacks from both sides, reports came Sept. 25 that the Russian and Syrian governments conducted air and artillery strikes on the U.S.-backed Syrian Democratic Forces in eastern Syria....