The campaign promise was that Mexico would pay for the wall. The promise wasn't that we would pay and then Mexico would reimburse us, maybe, based on some as-yet-to-be-negotiated, financial/tariff adjustment, smoke and mirrors, creative accounting gimmick. 

If I promise the world that you are going to buy me a new car, as soon as I write the check, I have lied. The DHS is going to start spending our money on this idiotic wall, so Trump lied.