Last night, US Government temporarily suspended all visa applications by Turkish citizens at the US diplomatic missions (except those for immigrant status) and about 2 hours later Turkish government reciprocated by temporarily suspending all visa applications (including evisa and visa-on-arrival) for US citizens to visit Turkey. "https://www.evisa.gov.tr/en/noevisa/". Those visitors who already have their evisas in hand will not be affected by this situation.
This situation would have to be temporary and I am sure would be resolved by diplomatic negotiations soon.
For further details you can have a look at: "hurriyetdailynews.com/turkey-suspends-us-vis…".