Of course it helps to know some of the backstory on the Kurds in Turkey.
For decades they have been a repressed minority, not allowed to use their language in schools and in public, etc. And they fought back. Finally Erdogan started to make peace overtures, restoring Kurdish in schools and names of towns and roads, etc. There was even negotiations to release the imprisoned Kurdish leader Ocalan. Perhaps the only good Erdogan policy ever.
But Kurdish political parties did well enough in elections to deny Erdogan a 2/3rds majority preventing him from pulling a Putin and changing the country from a parliamentary (term-limited PM) to a presidential system with more concentrated powers. So in order to keep and consolidate power, Erdogan reignited the war on Turkish Kurds, jailed their leaders, and banned their political parties. A fraudulent war because Kurds exercised their voting rights. Then with the Kurds sidelined, Erdogan called new elections in which he was able to achieve his 2/3rds coalition and re-write the constitution so he could continue with unchecked power. Reinstituting a war on a minority for political gain. Real cynical hardball ish.
These are the "terrorists" that Erdogan accuses the Syrian Kurds of aiding. Just a few short years ago they were Erdogan's partners in peace and a reasonable resolution was at hand, with the Kurds finally getting rights and a voice in Turkey. Erdogan is a malicious shit.
If Trump had any balls, he'd retaliate against Erdogan by calling for the establishment of Kurdistan, comprising Eastern Turkey, northeast Syria and northern Iraq. The national borders are just fairly arbitrary colonial lines drawn on a map long ago, often following Ottoman colonial districts.
It's clear that Erdogan doesn't respect the border lines. Well, lets move the border into Turkey by advocating the formation of a new Kurdistan state. Kurds are pretty much our best allies in the region, and that would get them back on our side. Give them Kirkuk, Iraq and that oil wealth could fund a Kurdish state. See how Erdogan likes that.