The reality was that the agreement gave Mr. Erdogan everything he had hoped for — he gained territory and avoided sanctions — and it looked like a complete cave-in by the United States. And Mr. Pence was the impassive, uncomfortable face of a losing deal…

One possible clue that an association with the agreement might not be a winner, especially for a Republican, came from Secretary of State Mike Pompeo, who arrived in Ankara on a separate plane from Mr. Pence, and made it clear he was there strictly in a support role to back up the vice president. (His trip also extended to Jerusalem and Brussels, and his plane departed before Mr. Pence’s.)…

Senior administration officials had expressed reservations about Mr. Pence going at all, arguing that sending him to meet with Mr. Erdogan was something of a reward to the Turkish president in and of itself, a chit that was better held for when more progress had been made on a deal.

They also noted that Mr. Erdogan was benefiting politically at home from his military operation in Syria, and were not sure what the negotiating strategy would be beyond threatening punishing economic sanctions.